The same amount of speed each second
A ball rolling down an inclined plane each second picks up ______.
It is always zero.
What is the value of the velocity of the ball when it reaches its maximum height?
It is always negative.
What is the acceleration of the ball when it is moving up, when it is at the maximum height, and when it is moving down?
A ball freely falling at 20 m/s will in the next second have a speed of ______.
Image shows c is a straight line down and the dots are close together and get farther apart.
Which of the motion diagrams in the figure below best matches the motion of the bungee jumper shown in the video?
Free fall acceleration is constant and has a value of 9.8 m/s2.
Which of the following best describes the acceleration of a bungee jumper during free fall?
All three cars are accelerating because the directions of their velocity vectors change constantly as they drive in a circle. In addition, the speeds of cars A and B are changing, which also indicates acceleration.
Three cars drive around a perfectly circular track. The speedometers in the figure below show the speed of each car over the same 10-s time interval. Which of the cars are accelerating?
B, A, D, C,
The average accelerations, from most positive to most negative, are as follows: (B) 4 m/s2, (A) 3 m/s2, (D) 2.5 m/s2, and (C) ?3 m/s2.
Four cars undergo acceleration as described by the data in the following table.
In its first second of free fall, a dropped softball will fall a vertical distance of
Galileo’s definition of speed was a breakthrough because he is acknowledged to be the first to consider ______.
A. Increase the tilt of the yellow track.
If the yellow track were tilted steeply enough, its ball could win. How might you go about calculating the necessary change in tilt?
Consider the video demonstration that you just watched. Which of the following changes could potentially allow the ball on the straight inclined (yellow) track to win? Ignore air resistance.
one of many ways of making discoveries
The scientific method of Galileo and Bacon is ______.
guides to thinking
Equations in Conceptual Physics are used mainly _______.
Ptolemy’s geocentric model was based on the idea that Earth is the center of the universe, while Copernicus’s heliocentric model was developed around the idea that the Sun is at the center. While these two models were based on opposing ideas, they shared a common belief in uniform circular motion and the use of epicycles. However, Copernicus’s heliocentric model does not use epicycles to explain retrograde motion like Ptolemy’s geocentric model. In order to explain retrograde motion, Copernicus uses the different orbital speeds of the planets as an explanation to the
backward motion of the planets in the sky.
Two competing models attempt to explain the motions and changing brightness of the planets: Ptolemy’s geocentric model and Copernicus’ heliocentric model.
Sort the characteristics according to whether they are part of the geocentric model, the heliocentric model, or both solar system models.
The geocentric model was compelling because it adhered to religious beliefs about Earth’s centrality in the universe. The heliocentric model was compelling because it provided a simpler explanation for observed motions in the solar system. Because both models adhered to the belief in perfect form and motion, they made inaccurate predictions of planetary motions over long periods of time. Since neither model made better predictions than the other, both remained viable.
Copernicus’s heliocentric model and Ptolemy’s geocentric model were each developed to provide a description of the solar system. Both models had advantages that made each an acceptable explanation for motions in the solar system during their time.
Sort each statement according to whether it is an advantage of the heliocentric model, the geocentric model, or both.
The geocentric model conformed to both the philosophical and religious doctrines of the time.
The heliocentric model did not make noticeably better predictions than the geocentric model.
From Earth, all heavenly bodies appeared to circle around a stationary Earth.
Ancient astronomers did not observe stellar parallax, which would have provided evidence in favor of the heliocentric model.
The geocentric model, in all of its complexity, survived scientific scrutiny for almost 1,400 years. However, in modern astronomy, scientists seek to explain the natural and physical world we live in as simply as possible. The complexity of Ptolemy’s model was an indicator that his theory was inherently flawed. Why, then, was the geocentric model the leading theory for such a long time, even though the heliocentric model more simply explained the observed motions and brightness of the planets?
an agreement between trained investigators
A fact in science is ______.
110 Sun diameters
The distance between Earth and the Sun is about
A scientific hypothesis deemed valid must have a test for proving it ______.
He discovered that a ball rolling down an incline and onto a horizontal surface would roll indefinitely.
What was the greatest discovery by Galileo during his inclined-plane experiments?
a non-zero net force
Newton said that something was needed to change the motion of an object. A clear reading of his first law tells us that what is needed is ______.
Which of the following is a vector quantity?
pointing in the same direction
The sum of two vectors is the largest when the two vectors point in the same direction.
The sum of two vectors is the largest when the two vectors are _____.
The x component of the resultant of two vectors is Ax+Bx.
The sum of the x components of vectors A and B in (Figure 1) is ___.
Arrow pointing up to the left
To find the resultant of two vectors, add them tail-to-tip and then draw the resultant vector from the tail of the first vector to the tip of the last vector.
Which of the choices shows the correct resultant of adding the two vectors A and B shown in (Figure 2) ?
What is the net force on a crate sliding at an unchanging speed when pushed with a steady force of 75 N?
Because the sled’s velocity is constant, the net force must be zero and the two horizontal forces must balance out.
Recall the portion of the video in which the girl pushes her brother on the sled at constant velocity. The pushing force she exerts on the sled is _____ the frictional force the ground exerts on the sled.
have constant velocity
When the net force is zero, the acceleration is zero, so the velocity must be constant. Note that zero velocity is simply a special case of constant velocity.
According to Newton’s first law, when the net force acting on an object is zero, the object must
An object moving in a straight line at constant speed has zero acceleration because the net force acting on it is also zero.
An elevator moves straight upward at a constant speed. Newton’s first law predicts that the net force acting on the elevator will _____.
when you hold the ball still in your hands after catching it
when you hold the ball still in your hands before it is thrown
When an object’s velocity is changing, the net force on it is not zero, even if it stops for an instant.
Imagine holding a basketball in both hands, throwing it straight up as high as you can, and then catching it when it falls. At which points in time does a zero net force act on the ball? Ignore air resistance.
Whenever a net force acts on an object, there is a change in the object’s _______.
The acceleration of object B is three times that of object A.
Since F = ma, the acceleration is given by a = F/m, so the object with the lower mass has a higher acceleration.
Object A has three times the mass of object B. Identical forces are exerted on the two objects. Which statement is true?
The velocity of the parachutist is not changing with time.
Since the net force is zero, the parachutist’s acceleration is zero, so the velocity is constant in time.
A parachutist is falling toward the ground. The downward force of gravity is exactly equal to the upward force of air resistance. Which statement is true?
An object far from any source of gravity still has mass, even if no forces of gravity are acting on it.
A kilogram is a measure of an object’s
less than 800 N
Since the scale is pushing upward with a strength less than the force of gravity, the net force is directed downward, causing the person to decelerate.
A person who weighs 800 N (about 180 pounds) is standing on a scale inside an elevator. The elevator is moving upward yet slowing down. The reading on the scale is __________.
greater than 800 N
Since the person is accelerating upward, the scale must be pushing upward more strongly than the force of gravity.
A person who weighs 800 N is squatting on a scale. Suddenly he starts jumping, extending his legs as quickly as possible, so that he can jump into the air. As the person is in the process of jumping (accelerating upward) the reading of the scale is ____________.
The ratio of the force of gravity exerted on an object to the object’s mass is the same.
The acceleration is given by a = F/m, so all objects fall at the same rate since the force of gravity is proportional to the object’s mass.
A bowling ball and a small marble will fall downward to the surface of the Moon at the same rate. Why?
the twin in the green jumpsuit
Since the twin in the green jumpsuit (going head first) has a smaller surface area plowing through the air, she must fall faster in order for the force of air resistance to have the same strength as the force of gravity.
Two identical twins are falling toward the ground. The twin in the green jumpsuit is going down head first, and the twin in the red jumpsuit is going down belly first. The two twins have the same mass. Which twin reaches the fastest terminal velocity?
The red parachutist has a higher terminal velocity.
Since the red parachutist is more massive, he experiences a stronger force of gravity acting downward. In order for the wind resistance to balance this stronger force, he must have a faster terminal velocity.
Two parachutists have identical parachutes open and are falling toward the ground. The parachutist with the red jumpsuit is much more massive than the parachutist with the blue jumpsuit. How do the terminal velocities of the two parachutists compare?
Since the elevator is not accelerating, the reading on the scale is the same as in the video.
Consider the video tutorial you just watched. Suppose that we duplicate this experimental setup in an elevator. What will the spring scale read if the elevator is moving upward at constant speed?
when the crate is pushed horizontally, whether sliding or not.
A crate sits at rest on a factory floor. Friction between the crate and floor occurs _______.
When units of newtons and kilograms are used for force and mass
When does the proportion form of Newton’s second law take the form of an equation?
is greater for a heavier person
Air resistance on a parachutist at terminal speed _______
inversely proportional to mass.
In considering proportions, acceleration is _______.
He continues to apply a steady force.
After he gets the block to move, what does Dr. Hewitt do to drag the block across the table at a steady rate?
Equal to 3 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block.
If Dr. Hewitt applies 3 N of force to keep the block moving at a steady rate, what must be the force of friction, and why?
Equal to 5 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block.
You are dragging a block on a surface with friction at a steady speed of 2 m/s and exert a force of 5 N to do so. What is the force of friction? Why?
The force that you need to apply to keep an object moving at a steady rate is equal to the force resisting the motion of the object.
What general rule can you conclude about the force needed to keep an object in motion at a steady rate?
opposite to the direction of sliding
The direction of the force of friction on a sliding crate is _______.
Which depends on gravity?
As a skydiver gains speed in falling through the air, air resistance _______.
The unit of mass is the kilogram, and the unit of weight is the _______.
Ball 1 and Ball 2 have equal acceleration.
Which ball has a greater acceleration as it drops toward the ground, and why?
Both Ball 1 and Ball 2 will reach the ground at the same time.
Which ball do you predict will reach the ground first?
Ball 1 and Ball 2 will be traveling equally fast when they hit the ground
Which ball will be traveling faster when it hits the ground?
the ratio of weight to mass is the same for each.
A 1-kg stone and a 10-kg stone have the same acceleration in free fall because _______.
are normally at right angles to each other
Force vector components for a sled pulled at an upward angle _______.
The magnitudes of both forces are the same.
A Volkswagen Bug and a Volvo truck have a head-on collision. Which statement is true?
Both ropes are equally likely to break.
Since the attached rope doesn’t have to support any weight (as it did in the vertical case), the tension is the same in both ropes
The magnitudes of both forces are the same.
both his weight and the pull on his cage
When Monkey Mo dangles by a rope and pulls on his cage, each at different angle from the vertical, the rope tension will be greater than _______.
A 7-N vector at an angle of 45° to the horizontal has a vertical component that is about _______.
The rocket’s speed is proportional to the ratio of the fluid’s mass to the rocket’s mass.
Suppose we repeat the experiment from the video, but this time we use a rocket three times as massive as the one in the video, and in place of water we use a fluid that is twice as massive (dense) as water. If the new fluid leaves the rocket at the same speed as the water in the video, what will be the ratio of the horizontal speed of our rocket to the horizontal speed of the rocket in the video after all the fluid has left the rocket? (Ignore air resistance.)
Momentum is a vector quantity.
An object’s momentum is equal to the product of its mass and its velocity.
The momentum of an object is a vector quantity, and is defined as the product of the object’s mass and its velocity.
In the opening scenes of the prelecture video, we outlined some of the key properties of momentum. Which of the following statements are consistent with these properties?
A 1700kg rhino charges at a speed of 50.0km/h. What is the magnitude of the average force needed to bring the rhino to a stop in 0.50s?
A 3.6-kg chihuahua charges at a speed of 3.3m/s. What is the magnitude of the average force needed to bring the chihuahua to a stop in 0.50s?
Shown below is a graph of a force applied to a small object as a function of time. If the object has a mass of 5.0kg and is at rest at t=0s, how fast is the object moving at t=4.0s?
her hand is made to bounce from the bricks.
Cassy can get more force on the bricks she breaks with a blow of her bare hand when _______.
Half of it
Imagine that you replace the block in the video with a happy or sad ball identical to the one used as a pendulum, so that the sad ball strikes a sad ball and the happy ball strikes a happy ball. The target balls are free to move, and all the balls have the same mass. In the collision between the sad balls, how much of the balls’ kinetic energy is dissipated?
None of it
Now, consider the collision between two happy balls described in Part A. How much of the balls’ kinetic energy is dissipated?
The “glue force” cancels the collision force.
During the collision, the force exerted by the glue (on the eight-ball) cancels the force exerted by the cue ball (on the eight-ball). Thus, the momentum of the eight-ball system is conserved because the net external force acting on it is zero.
You might be confusing an “isolated” system with a system subject to “zero net force.” No external forces act on an isolated system. Is that the case for the eight-ball? For further review, see the discussion of systems in the video.
The video shows an animated billiards experiment in which a cue ball strikes a glued-in-place eight-ball. Which of the following explains why the momentum of the eight-ball is conserved?
The net external force on the system is zero.
When the net external force on a system is zero, the system has zero acceleration and constant momentum.
Which statement must be true for the momentum of a system to be conserved?
Two of the equations express the conservation principle in a different way. The equation P? A,i+P? B,i=P? A,f+P? B,f states that the total momentum of the system is the same before and after the collision; the equation ?P? A+?P? B=0 states that the change in the total momentum of the system is zero.
Bumper cars A and B undergo a collision during which the momentum of the combined system is conserved. Which equation(s) correctly states the principle of conservation of momentum?
The right shoe
In each collision, the change in momentum of the puck has the same magnitude as the change in momentum of the shoe. The puck has a greater magnitude of change in momentum when it rebounds, so the right shoe must undergo a greater change in momentum than the left shoe!
While goofing off at the ice skating rink, a student takes off her shoes and places each of them on the ice. Her friend, a hockey player, then shoots a hockey puck at each shoe. The first puck immediately comes to rest after it collides with the left shoe. The second puck rebounds after it collides with the right shoe. If each hockey puck has the same incoming speed, which shoe has greater speed after the collision?
at the same rate.
By doubling the mass but keeping the velocities unchanged, we doubled the angular momentum of the two-puck system. However, we also doubled the moment of inertia. Since L=I ?, the rotation rate of the two-puck system must remain unchanged.
Suppose we replace both hover pucks with pucks that are the same size as the originals but twice as massive. Otherwise, we keep the experiment the same. Compared to the pucks in the video, this pair of pucks will rotate
It will take less time to return to the point from which it was released.
The pendulum will swing back and forth more quickly (with a shorter period) because it is oscillating in a stronger gravitational field than that on Earth.
Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is g=30 m/s2. When he releases the ball from chin height without giving it a push, how will the ball’s behavior differ from its behavior on Earth? Ignore friction and air resistance.
When one does twice the work in twice the time, the power expended is _______.
Which energy production method does not ultimately depend on the Sun?
the same magnitude and sign
The kinetic energy of a moving object is always positive, regardless of the direction it is moving in, or the coordinate system used.
opposite directions at the same speed. Their kinetic energies have ____.
When an object’s displacement has a component in a direction opposite that of a given force, that force does negative work on the object.
A motorcycle drives up a steeply inclined ramp. The work done on the motorcycle by the Earth’s gravitational force is ____.
the object’s final speed was the same as its initial speed
When the net work done on an object is zero, there is no overall change in the object’s kinetic energy.
During a certain time interval, the net work done on an object is zero joules. We can be certain that ____.
The final speed will be the same, regardless of which slide is used.
The person starts out with the same potential energy regardless of which slide she chooses, and all of this potential energy is converted to kinetic energy at the bottom of the slide. Therefore, the person must have the same kinetic energy at the bottom of each slide.
A person has a choice of sliding down one of three slides, which are shown to the left. All slides start at the same height above ground. Ignoring friction, for which slide will the final speed of the person at the bottom be the highest?
The 2-kg ball has more kinetic energy.
The kinetic energy is proportional to the ball’s mass times the speed squared. The 2-kg ball is moving twice as fast and is half as massive, so it will have twice as much kinetic energy as the 4-kg ball.
A 2-kg ball is moving with a speed of 4 m/s, and a 4-kg ball is moving with a speed of 2 m/s. What can you conclude about the kinetic energies of the two balls?
1.4 times as fast.
The ball is dropped from a distance twice as high, so it has twice as much energy (all of its energy is initially in the form of potential energy). This means that its final kinetic energy is twice as high. Since the kinetic energy is proportional to the square of the ball’s speed, its speed must be 2? faster.
A ball is dropped from a distance 5 m above the ground, and it hits the ground with a certain speed. If the same ball is dropped from a distance 10 m above ground, its final speed will be ________.
greater than the original value but less than twice
The force of gravity weakens as the distance from the center of Earth increases (for changes in height that are small compared to the radius of the Earth, gravity can be approximated as being constant). Because of this weakening, the gravitational potential energy does not increase as quickly with height when the object is far away. As a result, the object doesn’t lose twice as much potential energy when it falls twice as far.
An object is dropped from a distance of R=2REarth from Earth’s center, and it falls down and hits Earth’s surface. If the object is dropped from a distance R=3REarth (twice as far away from Earth’s surface), its kinetic energy right before hitting the ground would be _____ what it was before.
thermal energy would be zero.
Thermal energy is the total kinetic energy of a substance due to all the random vibrational motions of the individual atoms. If the temperature were zero, none of the atoms would be moving.
If an object had a temperature of absolute zero (0 K), its
As the cloud collapses, gravitational potential energy is converted into thermal energy, causing the gas to heat up.
A star forms when gravity causes a gas cloud to collapse. As the size of the cloud decreases, the temperature of the cloud _____________.
the conversion of rest-mass energy into radiative energy.
The electron and proton have rest-mass energy (as well as some kinetic energy). All of this energy is converted into radiative energy.
A positron is a particle similar to an electron, but with the opposite charge of an electron. If a positron and an electron collide, sometimes both the electron and positron disappear (annihilate), and two photons are created. This is an example of ____________.
The average speed of the hydrogen molecules is faster than that of the helium atoms, but it is less than two times faster.
Since the temperature is the same for both types of atoms, they have the same average kinetic energy, which is given by K=1/2mv2. Helium is twice as massive as hydrogen, so the average speed of the hydrogen atoms is 2? times higher than that of the helium atoms.
A gas containing both hydrogen molecules (each molecule contains two hydrogen atoms) and helium atoms has a temperature of 300 K. How does the average speed of the hydrogen molecules compare to the helium atoms?
Its acceleration is constant.
A body that is in free fall has only the force of gravity acting on it. The acceleration due to gravity is constant of 10m/s/s. The velocity is increasing as the object falls with 10m/s for every second.
When an object is released from rest and falls in the absence of friction, which of the following is true concerning its motion?
Net force is always m•a. In this case, the velocity is constant so the acceleration is zero and the net force is zero. Constant velocity motion can always be associated with a zero net force.
The amount of net force required to keep a 5-kg object moving rightward with a constant velocity of 2 m/s is ____.
Inertia is a body to keep doing what it is doing, therefor if the car comes to a stop your body was already moving and wants to keep moving. Inertia only depends on mass and is independent of acceleration, resistance and gravity.
If your automobile runs out of fuel while you are driving, the engine stops but you do not come to an abrupt stop. The concept that most explains why is
the velocity is zero, the acceleration is directed downward, and the force of gravity acting on the ball is directed downward.
At the top of the path the velocity has a magnitude of zero but it is changing direction due to acceleration. The acceleration acting on the ball during the entire path is the acceleration due to gravity (10m/s/s) and the only force (excluding air resistance) acting on it is the force due to gravity directed downward.
A ball is tossed vertically upward. When it reaches its highest point (before falling back downward),
magnitude and direction
Vector is any concept with a magnitude and direction
A force is a vector quantity because it has both
follow a straight-line path.
Newton’s first law: if the net force (the vector sum of all forces acting on an object) is zero, then the velocity of the object is constant (same speed and same direction…straight line)
Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to
The newton is a unit of
The standard metric unit of mass is the kilogram.
( Know this one. Kilograms is for mass and Newtons is for force.)
Mass depends on how much matter is present in an object. ( This is kind of a simple definition of mass but it does do the job (provided stuff means atoms or material).
The mass of an object is mathematically related to the weight of the object. (The weight of an object is the mass of the object multiplied by the acceleration of gravity of the object. Mass and weight are mathematically related by the equation: Weight (or Fgrav) = m•g)
Which of the following statements are true of the quantity mass? List all that apply.
mass is the same but weight is less
The acceleration due to gravity is lower on the Moon than on Earth. Which one of the following statements is true about the mass and weight of an astronaut on the Moon’s surface, compared to Earth?
The weight of an object is dependent upon the value of the acceleration of gravity. (The weight of an object is equal to the force of gravity acting upon the object. It is computed by multiplying the object’s mass by the acceleration of gravity (g) at the given location of the object. If the location of the object is changed, say from the Earth to the moon, then the acceleration of gravity is changed and so is the weight. It is in this sense that the weight of an object is dependent upon the acceleration of gravity.)
Weight refers to a force experienced by an object. (This statement is true in the sense that the weight of an object refers to a force – it is the force of gravity.)
The weight of an object would be less on the Moon than on the Earth.
( The weight of an object depends upon the mass of the object and the acceleration of gravity value for the location where it is at. The acceleration of gravity on the moon is 1/6-th the value of g on Earth. As such, the weight of an object on the moon would be 6 times less than that on Earth.)
Which of the following statements are true of the quantity weight?
A constant force causes an object to accelerate at 4 m/s2. What is the acceleration of an object with twice the mass that experiences the same force?
they have different speeds and different velocities.
Velocity is speed and direction, Jack and Jill are traveling in the same direction but they have different speeds, so they will have different velocities.
Jack and Jill are both traveling straight north. Jack is walking at 4 mph, while Jill is riding a bicycle at 12 mph. Regarding their speeds and velocities:
about 10 m/s
The acceleration of gravity is approximately 10 m/s/s. Acceleration represents the rate at which the velocity changes – in this case, the velocity changes by 10 m/s every second. So the speed will increase by the amount of 10 m/s every second.
A speedometer is placed upon a free-falling object in order to measure its instantaneous speed during the course of its fall. Its speed reading (neglecting air resistance) would increase each second by ____.
If an object has an acceleration of 0 m/s2, then one can be sure that the object is not ____.
moving faster than car B, but not necessarily accelerating.
All that is necessary is that car A has a greater speed (is moving faster). If so, it will eventually catch up and pass car B. Acceleration is not necessary to overcome car B; a car going 60 mi/hr at a constant speed will eventually pass a car going 50 mi/hr at a constant speed. Surely you have witnessed that while driving down a local highway.
If car A passes car B, then car A must be ____.
If an object is slowing down, then the direction of the acceleration vector is in the opposite direction as the direction which the object moves. (If the object were speeding up, the acceleration would be eastward.)
If an object is moving eastward and slowing down, then the direction of its velocity vector is ____.
As an object falls, it accelerates; this means that the speed will be changing. While falling, the speed increases by 10 m/s every second. The acceleration is a constant value of 10 m/s/s; thus, choice b should not be chosen.
As an object freely falls, its ____.
about 100 m/s.
Since the speed of a free-falling object increases by 10 m/s every second, the speed after ten of these seconds will be 100 m/s.
Ten seconds after being dropped from rest, a free-falling object will be moving with a speed of ____.
her velocity has a leftward direction and her acceleration has a leftward direction.
The car is heading leftward and the velocity is always in the same direction as the direction which the object moves. Since the car is speeding up, the acceleration is leftward. Whenever an object speeds up, its acceleration is in the same direction which the object moves. Whenever an object slows down, its acceleration is in the opposite direction which the object moves.
Renatta Oyle is again found driving her ’86 Yugo down Lake Avenue, leaving the following trail of oil drops on the pavement. If her car is moving from right to left, then ..
its the criminal regardless of the value of v0.
A gun is accurately aimed at a dangerous criminal hanging from the gutter of a building. The target is well within the gun’s range but the instant the gun is fired and the bullet moves with a speed v0, the criminal lets go and drops to the ground. What happens?
masses and distance apart.
The equation for gravitational force,
cites only masses and distances as variables. Rotation and atmospheres are irrelevant.
The force of gravity between two planets depends on their
Yes, due to motion alone
Speed being a scalar, and velocity being a vector quantity are irrelevant. Any moving object has both momentum and kinetic energy.
Must a car with momentum have kinetic energy?
The object moves in a spiral with a decreasing radius.
An object moving over a frictionless horizontal surface experiences a force. The force is always at right angles to the object’s velocity and increasing in magnitude. Which of the following is the best description of the motion of the object?
If you were moving up or down at a constant speed, your weight would not be more or less. It must be accelerating to cause a change in apparent weight.
If you weigh yourself in an elevator, you’ll weigh more when the elevator
masses are different.
When a cannon is fired, the accelerations of the cannon and cannonball are different because the
After the collision, the mass of the moving freight cars has doubled. Can you see that their speed is half the initial velocity of freight car A?
Freight car A is moving toward identical freight car B that is at rest. When they collide, both freight cars couple together. Compared with the initial speed of freight car A, the speed of the coupled freight cars is
less than g.
Acceleration of a non-free fall is always less than g. Acceleration will actually be (20 N – 5 N)/2 kg = 7.5 m/s2.
When a 20-N falling object encounters 5 N of air resistance, its acceleration of fall is
Radius points outward.
Acceleration points inward
Velocity follows a straight path.
Which of the following correctly indicates the relationship between the position, velocity, and acceleration vectors for Penny B at a particular instant?
the same as the lady’s speed at Point B.
If the free fall ride were in a vacuum and the lady dropped a small ball at Point A, the speed of the ball at Point B would be
Distance = (1/2) x acceleration x time x time
So: Distance = (1/2) x 10 m/s2 x 4 s x 4 s
So: Distance = 80m
What is the distance covered of a freely falling object starting from rest after 4 s?
the net force on the car is zero.
Consider a car at rest. We can conclude that the downward gravitional pull of the Earth on the car and the upward contact force of the Earth on it are equal and opposite because:
twice what it was before.
In the 17th century, Otto von Güricke, a physicist in Madgeburg, fitted two hollow bronze hemispheres together and removed the air from the resulting sphere with a pump.
Two eight-horse teams could not pull the halves apart even though the hemispheres fell apart when air was readmitted.
Suppose von Güricke had tied both teams of horses to one side and bolted the other side to a trunk of a large tree (which did not move). In this case, the tension on the hemispheres would be:
The locomotive’s force on the wagons is as strong as the wagon’s force on the locomotove but the frictional force on the locomotive is forward and large while the backward frictional force on the wagons is small.
A locomotive pulls a series of wagons. Which is the correct analysis of the situation?
smaller than the acceleration of the bullet.
Many people are familiar with the fact that a rifle recoils when fired. This recoil is the result of action-reaction force pairs. A gunpowder explosion creates hot gases that expand outward allowing the rifle to push forward on the bullet. Consistent with Newton’s third law of motion, the bullet pushes backwards upon the rifle. The acceleration of the recoiling rifle is …
The gain in kinetic energy, proportional to the square of the block’s speed at the bottom of the ramp, is equal to the loss in potential energy. This, in turn, is proportional to the height of the ramp.
A block initially at rest is allowed to slide down a frictionless ramp and attains a speed v at the bottom. To achieve a speed 2v at the bottom, how many times as high must a new ramp be?
Both take the same time.
Because force equals the time rate of change of momentum, the two balls lose momentum at the same rate. If both balls initially have the same momentum, it takes the same amount of time to stop them.
Suppose a ping-pong ball and a bowling ball are rolling toward you. Both have the same momentum, and you exert the same force to stop each. How do the time intervals to stop them compare?
The momentum change is the same for both vehicles
Conservation of momentum tells us that the changes in momentum must add up to zero. So the change in the car’s momentum must be equal to the change in the truck’s momentum, and the two changes must be in the opposite directions.
A compact car and a large truck collide head-on and stick together. Which undergoes the larger momentum change?
The cart comes to a stop when all of the cart’s kinetic energy is lost to friction. The frictional force times the stopping distance is equal to the cart’s initial kinetic energy.
A cart on an air track is moving at 0.5 m/s when the air is suddenly turned off. The cart comes to rest after traveling 1 m. The experiment is repeated, but now the cart is moving at 1 m/s when the air is turned off. How far does the cart travel before coming to rest?
a scalar quantity
always positive or zero
is by definition a quantity that can be only positive or equal to zero. It’s a scalar quantity, doesn’t have a direction, it’s a number that quantifies the “amount of motion” an object has.
Kinetic energy is:
These are all Newton’s Third Law pairs of forces, so they have to be equal.
Two toy trucks travelling at different constant speeds are about to collide. The two identical trucks are travelling in the same direction, and truck A is carrying a heavy load.
During the collision, will the magnitude of the force exerted on truck A by truck B be _____ the magnitude of the force exerted on truck B by truck A?
equal to the momentum of the heavy cart.
Momentum is equal to force times time. Because the forces on the carts are equal, as are the times over which the forces act, the final momenta of the two carts are equal.
Consider two carts, of masses m and 2m, at rest on an air track. If you first push one cart for 3 s and then the other for the same length of time, exerting equal force on each, the momentum of the light cart is
Act of throwing a piece of paper
Pushing a chair
Lifting a water bottle
Ball being dropped
Lifting a book
Which of the following situations is WORK being done?
twice as much
When an object is lifted 10 m, it gains a certain amount of potential energy. If the same object is lifted 20 m, its potential energy gain is
Both of you have the same amount of potential energy.
You and your friend want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy (U) of you and your friend, after you both reach the top, assuming that you and your friend have equal masses.
The kinetic energy is proportional to the square of the speed. Therefore, doubling the speed quadruples the kinetic energy.
When the speed of your car is doubled, by what factor does its kinetic energy increase?
less than 100
A ball is projected into the air with 100 J of kinetic energy. The kinetic energy is transformed into gravitational potential energy on the path towards the peak of its trajectory. When the ball returns to its original height, its kinetic energy is ____ Joules. Do consider the effects of air resistance
Let’s say the ball has inertial mass m and velocity v. The decrease in momentum in case (i) is 0 – mv = -mv (final momentum minus initial momentum). In case (ii), we find mv – 0 = +mv. In case (iii), we have m(-v) – mv = -2mv because the ball’s velocity is now in the opposite direction. So the magnitude of the change is greatest in the third case.
Consider these situations: (i) a ball moving at speed v is brought to rest; (ii) the same ball is projected from rest so that it moves at speed v; (iii) the same ball moving at speed v is brought to rest and then projected backward to its original speed. In which case(s) does the ball undergo the largest change in momentum?
Doubling the velocity doubles the magnitude of the momentum and increases the kinetic energy by a factor of four.
What does doubling an object’s velocity do to its momentum and to its kinetic energy?
Just as they leave the ground, the lighter frog is moving faster than the heavier frog.
Both frogs reach the same maximum height.
A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible. Which of the following statements about these frogs are correct? (There could be more than one correct choice.)
A bowling ball is mounted from a ceiling by way of a strong cable. It is drawn back and released, allowed to swing as a pendulum. As it swings from its highest position to its lowest position, the total mechanical energy is mostly conserved