Physics Conceptual Questions
You observe two identical balls of putty heading directly toward each other at equal speeds. What can you say about their total kinetic energy? a) They have zero total kinetic energy. b) Nothing. The kinetic energy of separate objects cannot be combined. c) They have some total amount of kinetic energy, with a magnitude d)They have twice the kinetic energy of either ball by itself. e) between zero and double the kinetic energy of either ball by itself.
d) They have twice the kinetic energy of either ball by itself. b/c They have the same mass and equal speeds so they have equal amounts of kinetic energy. Since kinetic energy is a scalar (not a vector), the direction that they are moving doesn't matter.
During a large, multi-object collision that involves object C, the change in the momentum of object C is equal to __________. a) the impulse exerted on object C by the last object to touch it b) the net impulse exerted on object C during the second half of the collision c) the impulse exerted on other objects by object C d) the net impulse exerted on object C
d) the net impulse exerted on object C
The impulse approximation is used in situations where __________. nswer no external forces are exerted on the system at all external forces on the system are present, but they are small compared to the large, brief internal forces between parts of the system no net external force is exerted on the system internal forces between parts of the system are small enough not to affect the momentum of any part of the system
external forces on the system are present, but they are small compared to the large, brief internal forces between parts of the system
In general, when a planet orbits a star, ______. it moves with a higher speed during some parts of its orbit and a slower speed during other parts. it speeds up continuously as it orbits. it slows down continuously as it orbits. it moves with the same speed during all parts of its orbit.
it moves with a higher speed during some parts of its orbit and a slower speed during other parts.
The angular momentum of a system is conserved during a certain process only if __________. no external torques are exerted on the system at all during that process no net external torque is exerted on the system during that process no internal torques between parts of the system are exerted at all during that process the angular momentum of each part of the system stays exactly the same during that process
no net external torque is exerted on the system during that process
Kepler's second law of planetary motion describes the area "swept out" by the line connecting a planet and the Sun during equal time intervals. The conceptual message of the law is that ______.
planets move faster when they are near the Sun, and move more slowly when they are farther away.
A bicycle wheel rotates counterclockwise and increases in angular velocity at a constant rate. What are the appropriate units for a measurement of the wheel's angular acceleration?
rad/s^2
If you divide a torque by a moment of inertia, which of the following are valid units for the resulting quantity? m/s2 N/kg N*m/kg rad/s2
rad/s^2
When an object is rotating, how is the tangential acceleration of a point on its outer edge (at a distance r from the axis of rotation) related to its angular acceleration?
tangential acceleration = angular acceleration x radius
When a volume stress is applied to a rigid body and the stress is small enough such that the object returns to its original shape when the stress is removed, then the ratio of stress/strain is equal to __________. a value that depends on the strength of the stress the shear modulus a value that depends on the amount of strain Young's modulus the bulk modulus
the bulk modulus
When a shear stress is applied to a rigid body and the stress is small enough such that the object returns to its original shape when the stress is removed, then the ratio of stress/strain is equal to __________. the shear modulus a value that depends on the amount of strain Young's modulus the bulk modulus a value that depends on the strength of the stress
the shear modulus
Two kids slide toward each other on ice (assumed frictionless). When they get close enough they grab onto each other. In this process __________. heir total angular momentum increases their total angular momentum becomes zero their total angular momentum is constant their total angular momentum decreases
their total angular momentum is constant
A wheel with a 3-m radius rotates with constant angular velocity = 2 rad/s. During 1 second, what is the wheel's angular displacement?
2 rad
A wheel with a 3-m radius rotates on a stationary axle with constant angular velocity = 2 rad/s. During 1 second, what is the distance traveled by a point on the outer edge of the wheel?
6 m
Kepler's third law of planetary motion states that which two quantities are related? A planet's mass and orbital period are related. A planet's orbital period and the size of the planet's orbit are related. A planet's radius and rotational period are related. A planet's mass and its order in the planetary system are related.
A planet's orbital period and the size of the planet's orbit are related.
An object on a rope is lowered at a steadily decreasing speed. Which is true? A. The rope tension is greater than the object's weight. B. The rope tension equals the object's weight. C. The rope tension is less than the object's weight. D. The rope tension can't be compared to the object's weight.
A. The rope tension is greater than the object's weight.
A ball rolls down an incline and off a horizontal ramp. Ignoring air resistance, what force or forces act on the ball as it moves through the air just after leaving the horizontal ramp? A. The weight of the ball acting vertically down. B. A horizontal force that maintains the motion. C. A force whose direction changes as the direction of motion changes. D. The weight of the ball and a horizontal force. E. The weight of the ball and a force in the direction of motion.
A. The weight of the ball acting vertically down.
The moment of inertia of an object depends on which of the following factors? The angular acceleration of the object Whether friction is present in the rotation The torque applied to the object How the mass of the object is distributed
How the mass of the object is distributed
The angular momentum of an object moving in a circle can be calculated using __________.
Iw or mvr
During a complex collision between many objects, including object A and object C, the impulse exerted on object A by object C is equal to __________. the change in the momentum of object A the change in the momentum of object C the impulse exerted on object C by object A None of the listed responses is correct.
None of the listed responses is correct.
Exoplanets (planets outside our solar system) are an active area of modern research. Suppose astronomers find such a planet that has the same mass as Earth, but has a radius that is about 10% less. Roughly, what acceleration due to gravity would you expect if you were standing on the surface of this new planet? Roughly 11 m/s2 Roughly 9 m/s2 Roughly 12 m/s2 Roughly 10 m/s2 (same as Earth)
Roughly 12 m/s2
The moment of inertia of an object depends on which of the following factors? The axis about which the object is rotated The angular acceleration of the object Where the accelerating force is applied The torque applied to the object
The axis about which the object is rotated
A person with mass M stands on a ladder of mass m that leans against a frictionless vertical wall and makes an angle of 53° measured from the horizontal. The ladder does not slip on the horizontal surface due to a static frictional force between the ladder and the ground. For this ladder, which of the statements is true? The ladder is in translational equilibrium and rotational equilibrium but is not in static equilibrium. The ladder is in translational equilibrium but not rotational equilibrium. The ladder is in rotational equilibrium but not translational equilibrium. The ladder is in static equilibrium.
The ladder is in static equilibrium
The units for momentum are __________.
kg*m/s
A bicycle wheel rotates counterclockwise at a constant rate. What are the appropriate units for a measurement of the wheel's angular velocity?
rad/s
When forces are exerted on an object, sometimes those forces will cause the object to be stretched, squeezed, or twisted. We define the deformation, which is the stretching, squeezing, or twisting of the object, as __________. tension shear stress compression strain
strain
According to Kepler's third law of planetary motion, if the Earth's orbit was twice as large as it is, how long would it take for the Earth to go around the Sun once About 3.6 times as long About 2.8 times as long About 4 times as long About 2 times as long
About 2.8 times as long
What are the appropriate units for stress?
Pa
Kepler's first law of planetary motion tells us that planets move in ellipses. If we picture the elliptical orbit of a planet orbiting the Sun, where does the Sun fit into the picture? The Sun is at one focus of the ellipse, with nothing at the other focus. The Sun is at the center of the ellipse, right where the long axis and the short axis of the ellipse cross. The Sun is on the opposite side of the ellipse from the planet. The Sun is at one focus of the ellipse, with the planet at the other focus.
The Sun is at one focus of the ellipse, with nothing at the other focus
The moment of inertia of an object depends on which of the following factors? Whether friction is present in the rotation The angular acceleration of the object Where the accelerating force is applied The total mass of the object
The total mass of the object
What is true about the work done by a conservative force? a) The work done by a conservative force will change the total mechanical energy of a system. b) The work done by a conservative force is always path independent. c) The work done by a conservative force is always path dependent. d) The work done by a conservative force will increase the internal energy of a system.
The work done by a conservative force is always path independent.
Suppose two people are pushing at different points on a merry-go-round. How do we account for their combined effects on the rotation of the merry-go-round? We add the torques caused by each person, accounting for direction, and use Newton's second law for rotation, . We add the forces they each exert, calculate a total torque, and use Newton's second law for rotation, . We add the magnitudes of their torques and use Newton's second law for rotation, . We add the magnitudes of their forces, calculate a total torque, and use Newton's second law for rotation, .
We add the torques caused by each person, accounting for direction, and use Newton's second law for rotation, (the sum of Torque is equal to Inertia x angular acceleration
When a tensile or compressive stress is applied to a rigid body and the stress is small enough such that the object returns to its original shape when the stress is removed, then the ratio of stress/strain is equal to __________. Young's modulus a value that depends on the amount of strain a value that depends on the strength of the stress the shear modulus the bulk modulus
Young's modulus
When forces are exerted on an object, sometimes those forces will cause the object to be stretched, squeezed, or twisted. We define the strength of the force that might cause an object to be stretched, squeezed, or twisted as __________. strain deformation exertion stress
stress
In which of the following situations is a net torque being created by the interactions described? A rubber ball is released on a ramp and begins rolling downward. A ball is released in mid-air and falls downward. A man is being lifted upward by an elevator. A woman climbs a ladder leaning against her house.
A rubber ball is released on a ramp and begins rolling downward. With the other examples, there was no rotation
In which of these processes is the angular momentum of the object conserved? A skydiver (the object), tucked into a ball and tumbling through the air, puts out her hands and stops her rotation relative to the ground. An ice-skater (the object), spinning with his arms outstretched, pulls in his arms, causing him to spin faster around his central axis. A football (the object) begins spinning around its central axis as it is thrown by a player. A car's wheel (the object) begins rotating around the axle as the car pulls away from a stop sign.
An ice-skater (the object), spinning with his arms outstretched, pulls in his arms, causing him to spin faster around his central axis. Each of the other examples applied torque, which does not conserve momentum. The ice skater changed his rotational motion, but not his momentum
A steel beam hangs from a cable as a crane lifts the beam. What forces act on the beam? A. Gravity. B. Gravity and tension in the cable. C. Gravity and a force of motion. D. Gravity and tension and a force of motion.
B. Gravity and tension in the cable.
An object on a rope is lowered at constant speed. Which is true? A. The rope tension is greater than the object's weight. B. The rope tension equals the object's weight. C. The rope tension is less than the object's weight. D. The rope tension can't be compared to the object's weight.
B. The rope tension equals the object's weight.
Which of the following is an important difference between an object's mass and its weight? Mass and weight have different units. Mass is determined by the environment of an object, while weight is a fixed property of the object. Mass is a type of force, weight is not. Weight is a direct measure of how much inertia an object has. Mass is not related to inertia.
Mass and weight have different units.
What is a valid unit for torque?
N*m
The standard units of momentum are kg*m/s. Which of these is an alternate way to express these units?
N*s
Can an object have more than one momentum at a given moment?
No, an object always has one unique velocity and one unique mass at any given moment.
A football is thrown in the usual way but in an airless environment. The ball spins as it flies along. Is the football's inertia creating a torque on the ball at this moment? Yes, the ball's inertia is what keeps the ball spinning as it moves. No, the ball's inertia is pushing it forward but is not creating a torque. Yes, the ball's inertia counteracts the natural tendency for the ball to stop rotating as it moves. No, inertia is not a force, so it cannot create a torque.
No, inertia is not a force, so it cannot create a torque.
A turntable spins on a frictionless axle with an unchanging speed. Does any part of the turntable exert a torque on any other part of the turntable? No, since the various parts of the turntable do not exert any forces on each other, they cannot exert torques on each other. No, since the entire object has the same angular motion, no internal torques are exerted by one part of the turntable on another part. Yes, these internal torques are what must be counteracted by the object's inertia in order for it to keep spinning. Yes, but since these internal torques cancel out, the angular motion of each part of the turntable stays the same.
No, since the entire object has the same angular motion, no internal torques are exerted by one part of the turntable on another part.
Exoplanets (planets outside our solar system) are an active area of modern research. Suppose astronomers find such a planet that has the same radius as Earth, but is about 10% less massive. Roughly, what acceleration due to gravity would you expect if you were standing on the surface of this new planet? Roughly 12 m/s2 Roughly 11 m/s2 Roughly 9 m/s2 Roughly 10 m/s2 (same as Earth)
Roughly 9 m/s2
A Blu-ray disc rotates counterclockwise and speeds up at a constant rate. How does the angular acceleration of point P compare to the angular acceleration of point Q if P is closer to the center and Q is closer to the outside.
The angular acceleration of point P is equal to the angular acceleration of point Q.
Suppose you are floating in deep space (in a space suit). You grab onto two identical toolboxes, one of which is full of metal tools and the other of which is empty. As you shake the two tool boxes around by their handles, which is the correct statement about what you would notice? The empty toolbox has a much smaller mass, so it is much easier to move it around. Both the empty toolbox and the full toolbox have zero weight, so they are both very easy to move around. The empty toolbox has a smaller weight, so it is much easier to move it around. Both the empty toolbox and the full toolbox have zero inertia, so they are both very easy to move around.
The empty toolbox has a much smaller mass, so it is much easier to move it around.
Which of the following forces is considered a conservative force? The force of tension from a rope The force of friction due to a surface The force due to a spring The force of someone pushing an object
The force due to a spring
A person with mass M stands on a ladder of mass m that leans against a frictionless vertical wall and makes an angle of 53° measured from the horizontal. The ladder does not slip on the horizontal surface due to a static frictional force between the ladder and the ground. Some of the forces exerted on the ladder can produce torques on the ladder. Using the contact point between the ladder and the ground as a reference, which force(s) exerted on the ladder produce counterclockwise torques? The force of the wall on the ladder and the static frictional force between the ladder and the ground. The weight of the ladder, the weight of the person, the static frictional force between the ladder and the ground. The force of the wall on the ladder The weight of the ladder, the weight of the person, and the force of the wall on the ladder The weight of the ladder and the weight of the person
The force of the wall on the ladder
When helping a friend move into a new home, you push a chair across the room. What do you know about the force that you exert on the chair?
The force you exert on the chair contributes to the overall change in kinetic energy of the system (the chair) with a positive amount and therefore does positive work on the system.
In order to calculate the torque exerted by object A on object B, what information is needed?
The location at which the force is applied and the force applied by A on B (both magnitude and direction)
Viewing an analog clock, what can you say about the angular momentum of the clock's two hands? The hour hand has greater angular momentum than the minute hand. The minute hand has the same angular momentum as the hour hand. The minute hand has greater angular momentum than the hour hand.
The minute hand has greater angular momentum than the hour hand. B/c: The minute hand has a greater angular velocity than the hour hand since the minute hand makes one revolution in an hour while the hour hand makes one revolution in twelve hours. Also, the minute hand is longer than the hour hand so it will have a greater moment of inertia (i.e. rotational inertia). Because the angular momentum is calculated with the product of the moment of inertia and the angular velocity (), the minute hand's angular momentum is greater.
What is required for a rigid body to be in static equilibrium? The rigid body must exhibit no translational motion and constant, non-zero rotational motion. The rigid body must exhibit no translational motion but can exhibit rotational motion. The rigid body must exhibit no rotational motion and constant, non-zero translational motion. The rigid body must exhibit no translational motion and no rotational motion. The rigid body must exhibit no rotational motion but can exhibit translational motion.
The rigid body must exhibit no translational motion and no rotational motion
Two objects are rolling down a ramp. They both have the same mass and the same radius, but one is a solid sphere and the other is a solid disk. Which object has the larger moment of inertia? We cannot tell without knowing the mass and radius. They have the same moment of inertia. The solid disk The solid sphere
The solid disk
A block slides on a horizontal frictionless table and is attached to a string that passes through a hole in the table. The block moves in a circular path around the hole. If you pull downward on the string and reduce the radius of the block's circular path, what happens to the block's speed? The speed decreases The speed increases The speed does not change The speed first increases, then decreases The speed first decreases, then increases
The speed increases. B/c the block's angular momentum is conserved. Since the radius of the block's circular path decreases, its speed must increase to keep the angular momentum constant, according to L = mvr.
What is required for a rigid body to be in rotational equilibrium? The sum of the torques due to all the forces exerted on the body must be constant and non-zero. The rigid body must exhibit no translational motion. The rigid body must exhibit no rotational motion. The sum of the torques due to all the forces exerted on the body must be zero. There can only be one torque due to all the forces exerted on the body.
The sum of the torques due to all the forces exerted on the body must be zero.
A person with mass M stands on a ladder of mass m that leans against a frictionless vertical wall and makes an angle of 53° measured from the horizontal. The ladder does not slip on the horizontal surface due to a static frictional force between the ladder and the ground. Some of the forces exerted on the ladder can produce torques on the ladder. Using the contact point between the ladder and the ground as a reference, which force(s) exerted on the ladder produce clockwise torques? The force of the wall on the ladder The weight of the ladder and the weight of the person The weight of the ladder, the weight of the person, and the static frictional force between the ladder and the ground The force of the wall on the ladder and the static frictional force between the ladder and the ground The weight of the ladder, the weight of the person, the force of the wall on the ladder
The weight of the ladder and the weight of the person
Exoplanets (planets outside our solar system) are an active area of modern research. Suppose you read an article stating that there is a newly discovered planetary system with three planets. The article states that the outermost planet (Planet C) goes all the way around its star in less time than the innermost planet (Planet A). According to Kepler's laws of planetary motion, is this possible?
This is not possible, since it would violate Kepler's third law of planetary motion.
As you stand facing a turntable, you reach out and push the near edge to the right, causing it to spin. Which statement best describes the angular momentum of the turntable? Viewed from below, the angular momentum would be negative. Viewed from below, the angular momentum would be positive. Viewed from anywhere, the angular momentum would be to the right. Viewed from anywhere, the angular momentum would be to the left.
Viewed from below, the angular momentum would be negative
When a wheel is "rolling without slipping" does any part of the wheel have an upward component to its velocity from the perspective of a person watching the wheel roll past them? Yes, every point on the "back side" of the wheel has an upward component to its motion from the perspective of a person watching the wheel roll past them. No, every point on the wheel has the same purely forward motion from the perspective of a person watching the wheel roll past them. Yes, every point on the "front side" of the wheel has an upward component to its motion from the perspective of a person watching the wheel roll past them. No, but some points on the wheel do have a downward component to their velocity from motion from the perspective of a person watching the wheel roll past them.
Yes, every point on the "back side" of the wheel has an upward component to its motion from the perspective of a person watching the wheel roll past them.
If you kick a big rock very hard while on the Earth, you might break a toe. If you kicked a similar rock while on the Moon, would you still be in danger of breaking your toe? Yes, this is about the rock's mass, which is the same on the Moon as on the Earth. Yes, this is about the rock's weight, which is the same on the Moon as on the Earth. No, this is about the rock's weight, which is much smaller on the Moon than it is on the Earth. No, this is about the rock's mass, which is much smaller on the Moon than it is on the Earth.
Yes, this is about the rock's mass, which is the same on the Moon as on the Earth.
If some quantity, let's call it "Z," is conserved for a certain system, during a certain process, that must mean __________.
any change in Z for parts of the system during the process is offset by an equal but opposite change for the Z of other parts of the system
The mechanical energy of a system is conserved during a certain process only if __________. a) the mechanical energy of each part of the system stays exactly the same during that process b) non-conservative forces do zero total work on the system during that process c) no external forces are exerted on the system at all during that process d) non-conservative forces are not exerted on the system during that process
b) non-conservative forces do zero total work on the system during that process
A boy sits on the edge of a stationary merry-go-round. His dog runs along the ground and jumps into his arms in such a way that the merry-go-round starts to spin. After the dog has landed and the merry-go-round is spinning, __________.
both the merry-go-round and the dog have non-zero angular momentum around the merry-go-round's axle B/c both objects are moving in a circle around the axle of the merry-go-round, they both have non-zero angular momentum around that axle.
When an object is rotating, how is the linear velocity of a point on its outer edge (at a distance r from the axis of rotation) related to its angular velocity?
v = r w
A bicycle wheel rotates counterclockwise at a constant rate. You can use one of the wheel's spokes to measure the wheel's angular displacement. What are the appropriate units for this measurement?
radians (rad)
When an object is rotating, how is the linear velocity of a point on its outer edge (at a distance r from the axis of rotation) related to its angular velocity?
v = rw
A weightlifter brings a 400-N barbell upward from his shoulders to a point 50 cm higher at a steady speed. During this process, what is the total work done on the barbell? a) -200 joules b) -400 joules c) 0 joules d) 200 joules e) 400 joules
0 Joules b/c moving at constant speed so change in kinetic energy is 0 which means Work is 0
A wheel is rotating counterclockwise, which we will define as the positive direction, at an angular velocity of 2 rad/s. If the wheel then experiences a clockwise angular acceleration of 1 rad/s2, what is the wheel's angular velocity 3 seconds later?
1 rad/s clockwise
A wheel is rotating counterclockwise, which we will define as the positive direction, at an angular velocity of 2 rad/s. If the wheel then experiences a counterclockwise angular acceleration of 1 rad/s2, what is the wheel's angular velocity 3 seconds later?
5 rad/s counterclockwise
A constant force causes an object to accelerate at 4 m/s. What is the acceleration of an object with twice the mass that experiences the same force? A. 1 m/s B. 2 m/s C. 4 m/s D. 8 m/s E. 16 m/s
B. 2 m/s
In which of these processes is the momentum of the object conserved? A train (the object) goes around a curve at a steady speed. An asteroid (the object) accelerates steadily toward the moon. A car (the object) pulls away from a stop sign. A skydiver (the object) with her parachute deployed falls toward the ground at a steady speed. A cyclist (the object) collides with a pedestrian.
A skydiver (the object) with her parachute deployed falls toward the ground at a steady speed. Because... Having a quantity be conserved means that it doesn't change. In order for momentum to be conserved it must have an unchanging mass and velocity (including both speed and direction). When a cyclist collides with a pedestrian it is reasonable to talk about the momentum of the system (both the cyclist and pedestrian) as being conserved, but the cyclist will change speed and probably direction, so the momentum of just the cyclist will not be conserved. As a car pulls away from a stop sign, it is speeding up, increasing the magnitude of its momentum. As an asteroid accelerates toward the moon, it is speeding up, increasing the magnitude of its momentum. As a train goes around a curve at a steady speed, it is changing the direction of its momentum.
A book rests on a horizontal table. Gravity pulls down on the book. You may have learned something in a previous physics class about an upward force called the"normal force." Deep in your heart, do you really believe the table is exerting an upward force on the book? A. Yes, I'm quite confident the table exerts an upward force on the book. B. No, I don't see how the table can exert such a force. C. I really don't know.
A. Yes, I'm quite confident the table exerts an upward force on the book.
Viewing an analog clock, what can you say about the direction of the angular momentum of the clock's two hands? The minute hand has negative angular momentum, but the hour hand has positive angular momentum. Both hands have angular momentum that is positive. Both hands have angular momentum that is negative. The minute hand has positive angular momentum, but the hour hand has negative angular momentum
Both hands have angular momentum that is negative
A bobsledder pushes her sled across horizontal snow to get it going, then jumps in. After she jumps in, the sled gradually slows to a halt. What forces act on the sled just after she's jumped in? A. Gravity and kinetic friction. B. Gravity and a normal force. C. Gravity and the force of the push. D. Gravity, a normal force, and kinetic friction. E. Gravity, a normal force, kinetic friction, and the force of the push.
D. Gravity, a normal force, and kinetic friction.
Two hockey players collide on the ice. Which statement reflects how we can apply conservation of momentum to this situation? From several seconds before the collision until several seconds after the collision the total momentum of the two players (the system) is a conserved quantity. During the very brief collision the total momentum of the two players (the system) is a conserved quantity. During the very brief collision the momentum of each player is a conserved quantity. From several seconds before the collision until several seconds after the collision the momentum of each player is a conserved quantity.
During the very brief collision the total momentum of the two players (the system) is a conserved quantity.
Standing on a turntable, a professor is spinning holding a dumbbell in each hand with his arms out sideways, as shown. The professor then quickly lowers his arms, so that the dumbbells are by his legs. Consider the realistic situation in which there is a small amount of friction acting to slow down the turntable. Which statement reflects how we can apply conservation of angular momentum to this situation? From several seconds before lowering his arms until several seconds after lowering his arms the angular momentum of each part of the system (turntable, professor, and dumbbells) is a conserved quantity. During the very brief process of lowering his arms the angular momentum of each part of the system (turntable, professor, and dumbbells) is a conserved quantity. During the very brief process of lowering his arms the total angular momentum of the turntable, professor, and dumbbells (the system) is a conserved quantity. From several seconds before lowering his arms until several seconds after lowering his arms the total angular momentum of the turntable, professor, and dumbbells (the system) is a conserved quantity.
During the very brief process of lowering his arms the total angular momentum of the turntable, professor, and dumbbells (the system) is a conserved quantity.
The figure shows a wheel of radius R made from a thin hoop and 8 spokes. Assuming the inner hub can be neglected, what is the correct expression for the moment of inertia of this wheel around its central axis? I = m(hoop) xR^2 + 8(1/3 x m(spoke) x R^2) I = (m(hoop) + 8m(spoke))R^2 I = m(hoop) xR^2 + 8(1/12 x m(spoke) x R^2)
I = m(hoop) xR^2 + 8(1/3 x m(spoke) x R^2)
Two wheels, A and B, have the same shape and size, but wheel A has twice the mass of wheel B. How do the moments of inertia (around the axis of symmetry) of the two wheels compare? I(A) = I(B) I(A) = 4 x I(B) I(A) = 1/2 x I(B) I(A) = 2 x I(B)
I(A) = 2 x I(B)
Two wheels, A and B, have the same basic shape and the same overall mass, but wheel A has twice the radius of wheel B. How do the moments of inertia (around the axis of symmetry) of the two wheels compare? I(A) = I(B) I(A) = 4 x I(B) I(A) = 1/2 x I(B) I(A) = 2 x I(B)
I(A) = 4 x I(B)
A neutron star is a compact star that forms from the gravitational collapse of a very massive star. The inward gravitational force can be so strong that a neutron star that started out to be twice as large as our Sun might have a radius of 13 km after collapse. What is true about the angular momentum of the neutron star during its collapse?
Its angular momentum is constant during its collapse.
The magnitude of the angular momentum of a rotating wheel can be directly calculated using __________.
L = Iw but not L = mvr because this cannot be applied directly to the entire object
When a wheel is "rolling without slipping," does any part of the wheel go backwards from the perspective of a person watching the wheel roll past them?
No, from their perspective at any given instant every part of the wheel is either moving forward or is at rest. B/c Under these conditions, at any given instant, the lowest point on the wheel is at rest relative to the ground, and the rest of the wheel is moving forward (at varying speeds, depending on which part of the wheel you consider).
When an object is rotating, how is the tangential acceleration of a point on its outer edge (at a distance r from the axis of rotation) related to its angular acceleration?
One radian is the angle at which the arc s has the same length as the radius r.
A neutron star is a compact star that forms from the gravitational collapse of a very massive star. The inward gravitational force can be so strong that a neutron star that started out to be twice as large as our Sun might have a radius of 13 km after collapse. What happens to the angular velocity of the neutron star during its collapse?
The angular velocity increases.
A brother and sister are riding on a merry-go-round at the park. The brother rides on the outer edge of the merry-go-round and the sister rides closer to the center. While the merry-go-round rotates with a constant angular velocity, who has the greatest centripetal (radial) acceleration?
The brother has the greatest centripetal (radial) acceleration.
A brother and sister are riding on a merry-go-round at the park. The brother rides on the outer edge of the merry-go-round and the sister rides closer to the center. While the merry-go-round rotates with an increasing angular velocity, who has the greatest tangential acceleration?
The brother has the greatest tangential acceleration.
A block slides along a rough surface and comes to a stop. What can you conclude about the frictional force exerted on the block? a) The frictional force does no work on the block and doesn't change its kinetic energy. b) The frictional force does negative work on the block and decreases its kinetic energy. c) The frictional force does positive work on the block and increases its kinetic energy. d) The frictional force does positive work on the block and decreases its kinetic energy. e) The frictional force does negative work on the block and increases its kinetic energy.
The frictional force does negative work on the block and decreases its kinetic energy.
Two wheels, A and B, are both shaped like uniform disks and have the same overall mass, but wheel A has twice the radius of wheel B. How do we calculate the moments of inertia (around the axis of symmetry) for each wheel? The moments of inertia are both calculated using I = mr^2 for their respective masses and radii. The moments of inertia are both calculated using I = 1/2 mr^2 for their respective masses and radii.
The moments of inertia are both calculated using I = 1/2 mr^2 for their respective masses and radii.
Playing in the rain, a little girl tackles a little boy. Just before she tackles him, the boy is running east at 3 m/s and the girl is running south at 4 m/s. After the tackle, the girl holds on and the two slide on the wet grass. Our system consists of just the two children. Immediately after the tackle, what can we say about how the momenta of each child compare? a) The momentum of both children will be in the same direction. b) The momentum of both children will be the same. c) The momentum of both children will be zero. d) The total momentum of the system will be zero, but the momentum of each child will not be zero.
The momentum of both children will be in the same direction. b/c Unless the two children happen to have exactly the same mass, they will not have equal momenta.
Which of the following describes the way rotational and translational motion are related to each other when a wheel is "rolling without slipping"? The tangential speed of the rim of the wheel relative to the wheel's axle is equal to the angular speed of the wheel's axle relative to the ground. The angular speed of the rim of the wheel relative to the wheel's axle is equal to the speed of the wheel's axle relative to the ground. The tangential speed of the rim of the wheel relative to the wheel's axle is equal to the speed of the wheel's axle relative to the ground. The angular speed of the rim of the wheel is equal to the tangential speed of the rim of the wheel relative to the wheel's axle.
The tangential speed of the rim of the wheel relative to the wheel's axle is equal to the speed of the wheel's axle relative to the ground.
Two cars experience a collision on a city road. Both drivers are using their brakes when the cars hit. Which statement is true? a) Using the impulse approximation, conservation of momentum can be applied to the very brief time period of the collision itself (giving approximate results). b) Using the momentum approximation, conservation of momentum can be applied to the time period leading up to the collision (giving approximate results) but not to the collision itself. c) Friction from the road does not change the fact that the momentum of the two cars will be perfectly conserved during the collision. d) Conservation of momentum cannot be applied at all.
Using the impulse approximation, conservation of momentum can be applied to the very brief time period of the collision itself (giving approximate results).
As you stand facing a merry-go-round, you reach out and push it to the left. Which statement best describes the angular momentum of the merry-go-round? Viewed from above, the angular momentum would be positive. Viewed from anywhere, the angular momentum would be to the left. Viewed from above, the angular momentum would be negative. Viewed from anywhere, the angular momentum would be to the right.
Viewed from above, the angular momentum would be negative. B/c it is moving clockwise
A young girl and her father take turns pushing open a big swinging gate. To do so, each person applies a torque to the gate around its hinges. She has studied some physics and is a careful thinker; is it possible for her to apply a larger torque than her father does? No, she and her father will always exert the same torque because they are both pushing the gate open. No, since the force she exerts is smaller than the force her father exerts, she cannot produce a larger torque than he does. Yes, by exerting her force further from the gate's hinge than her father does Yes, by exerting her force in a direction that is more parallel to the gate than her father's force
Yes, by exerting her force further from the gate's hinge than her father does
A turntable is spinning on a frictionless axle when a ball of putty is dropped onto it from above. The putty sticks to the turntable when it lands. Is angular momentum conserved for the turntable and putty (the system) during this process? Yes, since the external forces (gravity and forces from the axle) do not cause any torque around the axle of the turntable, the angular momentum of the system is conserved. Yes, since gravity is not acting on the system, the angular momentum of the system is conserved. No, since frictional forces are acting between parts of the system, the angular momentum of the system is conserved. No, since external forces (gravity and forces from the axle) are acting on the system, the angular momentum of the system is not conserved.
Yes, since the external forces (gravity and forces from the axle) do not cause any torque around the axle of the turntable, the angular momentum of the system is conserved.
If some quantity, let's call it "Z," is conserved for a certain system, during a certain process, that must mean __________.
Z for that system does not change in any way during that process
After getting a flat tire, one of the wheels on a car has been replaced with a wheel that is the same shape as the others, but it is made from lighter materials and has a smaller total mass. As the car drives along the road, the lighter wheel's angular momentum will have __________ magnitude compared to the other wheels on the car. a smaller a larger an equal
a smaller
A weightlifter exerts an upward force on a 1000-N barbell and lifts the barbell 1 meter upward in 2 seconds. Approximately how much power does the weightlifter exert on the barbell during this time? a) 1000 watts b) 500 watts c) 5000 watts d) 0 watts
b) 500 watts b/c Power is the rate at which work is done, or . If we assume the weightlifter applies a force that is almost equal to the weight of the barbell, then he does 1000 J of work, which comes from multiplying the force he exerts on the barbell and the barbell's displacement. The power is determined by dividing the work by the time interval in which the work was done, which is 2 seconds.
A block of mass m is attached to a horizontal spring and rests on a flat, smooth surface as seen in the figure. If you push on the block in the negative x-direction and compress the spring, what is true about the work done by the spring on the block during this motion? a) The spring does positive work on the block because the potential energy in the spring increases. b) The spring does negative work on the block because the spring force is in the opposite direction of the block's displacement. c) The spring does negative work on the block because the potential energy in the spring decreases. d) The spring does positive work on the block because the spring force is in the same direction as the block's displacement. e) The spring does no work on the block during this motion.
b) The spring does negative work on the block because the spring force is in the opposite direction of the block's displacement.
A variety of forces are applied to an object such that the net force does positive work on that object. What can you conclude about the speed of the object? a) When the total work done on the object is positive, the object will stop. b) When the total work done on the object is positive, the object's speed will increase. c) When the total work done on the object is positive, the object's speed will decrease. d) When the total work done on the object is positive, the object's speed will be constant.
b) When the total work done on the object is positive, the object's speed will increase.
The image shows two balls about have a head-on collision. Ball A has a mass m and speed of 2v, whereas ball B has mass 2m and speed v. Our system consists of just the two balls and is isolated from external forces. Just after the collision __________. a) both ball A and ball B must rebound with the same speed they had before the collision b) the total momentum of the system must be zero c) either ball A or ball B must be at rest d) both ball A and ball B must be at rest
b) the total momentum of the system must be zero
In both figures, a particle of mass m, is released from rest at a height, h. In figure (a), the particle is dropped straight downward and in figure (b) the particle is released from rest and slides down a ramp with a rough surface. Which particle, the one in figure (a) or (b), will have more kinetic energy at the bottom? a) The particles will have the same kinetic energy, but the particle in figure (b) will be moving faster at the bottom. b) The particle in figure (b) will have more kinetic energy than the particle in figure (a) at the bottom. c) The particle in figure (a) will have more kinetic energy than the particle in figure (b) at the bottom. d) The particles will have the same kinetic energy, but the particle in figure (a) will be moving faster at the bottom. e) Both particles will have the same kinetic energy at the bottom.
c) The particle in figure (a) will have more kinetic energy than the particle in figure (b) at the bottom b/c The kinetic energy of the particle when it gets to the bottom will be equal to the gravitational potential energy it started with: mgh. But in figure (b), friction—a non-conservative force—acts on the particle and decreases its total mechanical energy, converting some mechanical energy into thermal energy. As a result, this particle has less mechanical energy and therefore less kinetic energy than the particle in figure (a) when it gets to the bottom of the ramp.
What is true about the work done by a non-conservative force? a) The work done by a non-conservative force will always decrease the mechanical energy of a system. b) The work done by a non-conservative force will always decrease the internal energy of a system. c) The work done by a non-conservative force will always change the total mechanical energy of a system. d) The work done by a non-conservative force will always increase the mechanical energy of a system. e) The work done by a non-conservative force will always increase the internal energy of a system.
c) The work done by a non-conservative force will always change the total mechanical energy of a system.
When you lift a book upward off of a table, what is true about the work done on the book by the force of gravity? a) The work done by the force of gravity is positive and proportional to the upward displacement of the book. b) The work done by the force of gravity is negative and constant, regardless of the magnitude of the upward displacement. c) The work done by the force of gravity is negative and proportional to the upward displacement of the book. d) The work done by the force of gravity is positive and does not depend on the magnitude of the upward displacement.
c) The work done by the force of gravity is negative and proportional to the upward displacement of the book.
You observe two identical balls of putty headed directly toward each other at the same speed; what can you say about their total momentum? a) They have some total amount of momentum, with a magnitude between zero and double the momentum of either ball by itself. b) They have twice the momentum of either ball by itself. c) They have zero total momentum. d) Nothing. The momentum of separate objects cannot be combined.
c) They have zero total momentum.
In which of these processes is the total energy of the system conserved? a) A car (the system) slams on its brakes and comes screeching to a stop. b) A train car (the system) is pulled up a hill by a locomotive. c) Two balls of putty (the system) collide in midair and stick together. d) A rock (the system) falls through air and lands with a thud on the ground.
c) Two balls of putty (the system) collide in midair and stick together. because... When two balls of putty (the system) collide in midair and stick together the total energy of the system is conserved. As long as the system has no total work done on it by external forces, the total energy will always be conserved. The balls of putty exert non-conservative forces on each other, meaning the mechanical energy of the system will not be conserved, but even non-conservative forces still conserve energy. When a rock (the system) falls through air and lands with a thud on the ground, there is total work done on the rock by Earth's gravity, by air resistance, and by the impact force from the ground. Therefore the rock's total energy is not conserved. When a car (the system) slams on its brakes and comes screeching to a stop, there is total work done on the car by friction with the road. Therefore the car's total energy is not conserved. When a train car (the system) is pulled up a hill by a locomotive, there is total work done on the train car by Earth's gravity and by the locomotive (and perhaps by other forces as well). Therefore the train car's total energy is not conserved.
If Quantity X is conserved for a certain system and during a certain process, that means__________. a) Any change in Quantity X for that system during that process is offset by an equal but opposite change for the Quantity X of the surroundings b) the value of Quantity X for each part of the system must change in the same way during that process c) quantity X for that system does not change in any way during that process d) the value of Quantity X for each part of the system does not change during that process
c) quantity X for that system does not change in any way during that process
Without external torques an object __________. cannot change its own angular velocity even by rearranging its mass distribution can change its angular momentum by rearranging its mass distribution can change its own angular velocity by rearranging its mass distribution can change the velocity of its center of mass by rearranging its mass distribution
can change its own angular velocity by rearranging its mass distribution
Without external torques an object __________. can increase or decrease its own angular momentum can decrease but not increase its own angular momentum cannot change its own angular momentum can increase but not decrease its own angular momentum
cannot change its own angular momentum
A weightlifter exerts an upward force on a 1000-N barbell and holds it at a height of 1 meter for 2 seconds. Approximately how much power does the weightlifter exert on the barbell during this time? a) 500 watts b) 2000 watts c) 1000 watts d) 0 watts
d) 0 watts
Which of the following forces is considered a conservative force? a) The force of someone pushing an object b) The force of friction due to a surface c) The force of tension from a rope d) Gravity
d) Gravity
A block of mass m is attached to a horizontal spring and rests on a flat, smooth surface as seen in the figure. If you push on the block in the negative x-direction and compress the spring, what is true about the potential energy stored in the spring during this motion? a) The potential energy in the spring is zero. b) The potential energy in the spring decreases because the spring does negative work on the block. c) The potential energy in the spring increases because the spring does positive work on the block. d) The potential energy in the spring increases because the spring does negative work on the block. e) The potential energy in the spring decreases because the spring does positive work on the block.
d) The potential energy in the spring increases because the spring does negative work on the block.
A block of mass m is attached to a horizontal spring and rests on a flat, smooth surface as seen in the figure. The block can be pushed in the negative x-direction to compress the spring or pulled in the positive x-direction to stretch the spring. Where along the x-axis does the block have to be for the spring to have zero potential energy? a) The spring always has non-zero potential energy no matter where the block is located. b) The spring has zero potential energy when the block is at either x = ±xmax, where the spring is stretched/compressed to its maximum value. c) The spring has zero potential energy when the block is at x = +xmax, where the spring is stretched to its maximum value. d) The spring has zero potential energy when the block is at x = 0, where the spring is neither stretched nor compressed.
d) The spring has zero potential energy when the block is at x = 0, where the spring is neither stretched nor compressed.
The image shows two balls (1 and 2) that are going to collide as they approach the point marked . Ball 1 has a mass of 2m and speed v, while ball 2 has mass m and speed 2v. Both balls are moving at 45º angles with respect to the vertical. Our system consists of just the two balls and is isolated from external forces. Just before the collision a) the momentum of the two balls is the same b) the total momentum of the system is zero c) the horizontal components of the momentum of the two balls are the same d) the total horizontal component of the momentum of the system is zero
d) total horizontal component of the momentum of the system is zero b/c The magnitude of each ball's momentum is the same and since they have symmetric angles relative to the vertical direction, they will both have the same magnitude x-component, given by . Since their horizontal components of momentum are oppositely directed, they will cancel out and the total horizontal component of the momentum of the system is zero.
When helping a friend move into a new home, you push a chair across the room. What do you know about the force of gravity applied to the chair? a) The force of gravity applied to the chair increases the energy of the system (the chair) and therefore does positive work on the system. b) The force of gravity applied to the chair decreases the energy of the system (the chair) and therefore does positive work on the system. c) The force of gravity applied to the chair decreases the energy of the system (the chair) and therefore does negative work on the system. d) The force of gravity applied to the chair increases the energy of the system (the chair) and therefore does negative work on the system. e) The force of gravity applied to the chair does not change the energy of the system (the chair) and therefore does no work on the system.
e) The force of gravity applied to the chair does not change the energy of the system (the chair) and therefore does no work on the system.
Momentum __________. is a vector but can only have a magnitude and not a direction is a scalar, with a magnitude and direction is a vector, with a magnitude and a direction can be positive or negative but is not a vector
is a vector, with a magnitude and a direction
The units of angular momentum are __________.
kg*m2/s
If the wheels from two different kinds of car have the same mass, same radius, and same angular velocity, they __________. must have the same angular momentum might have the same angular momentum, but might not cannot have the same angular momentum
might have the same angular momentum, but might not
If two cars have the same mass and speed they __________. might have the same momentum but might not must have the same momentum cannot have the same momentum
might have the same momentum but might not
The momentum of a system is conserved during a certain process only if __________. no internal forces between parts of the system are exerted at all during that process no external forces are exerted on the system at all during that process no net external force is exerted on the system during that process the momentum of each part of the system stays exactly the same during that process
no net external force is exerted on the system during that process
The image shows a gear and a disk, each rotating as shown. The disk has twice the angular speed that the gear has (), and has one-half the moment of inertia (i.e. rotational inertia) that the gear has (). The two are pushed together (along the dotted line) until they make contact and begin to rotate together. Just before they make contact __________. the gear has an angular momentum with a larger magnitude than that of the disk the disk has an angular momentum with a larger magnitude than that of the gear the gear and disk have the same magnitude of angular momentum, but not the same direction the gear and disk have the same angular momentum
the gear and disk have the same angular momentum
The image shows a gear and a disk, each rotating as shown. The disk has twice the angular speed that the gear has (), and has one-half the moment of inertia (a.k.a. rotational inertia) that the gear has (). The two are pushed together (along the dotted line) until they make contact and begin to rotate together. After they make contact and begin to rotate together _____. the disk has an angular momentum with a larger magnitude than that of the gear the gear and disk have the same magnitude of angular momentum, but not the same direction the gear has an angular momentum with a larger magnitude than that of the disk the gear and disk have the same angular momentum
the gear has an angular momentum with a larger magnitude than that of the disk Once rotating together, they will have the same angular velocity, but with different moments of inertia, they will have different angular momentums (L=Iw)
A boy sits on the edge of a stationary merry-go-round. His dog runs along the ground and jumps into his arms in such a way that the merry-go-round starts to spin. While the dog is in the air and about to land in his arms, __________. the merry-go-round has a non-zero angular momentum around its axle, but the dog has zero angular momentum around that same axle the merry-go-round has zero angular momentum around its axle, and the dog has zero angular momentum around that same axle the merry-go-round has zero angular momentum around its axle, but the dog has a non-zero angular momentum around that same axle the merry-go-round has a non-zero angular momentum around its axle, and the dog has a non-zero angular momentum around that same axle
the merry-go-round has zero angular momentum around its axle, but the dog has a non-zero angular momentum around that same axle
The change in an object's momentum during a certain time interval is equal to __________. a) the net force exerted on the object times the distance the object travels in that time b) the change in the net force exerted on the object times the duration of the time interval c) the net force exerted on the object times the duration of the time interval d) the change in the speed of the object times the mass of the object
the net force exerted on the object times the duration of the time interval
The momentum of an object is defined as __________.
the object's mass times its velocity
how angular displacement related to angular velocity?
theta = angular velocity x change in time
A bicycle wheel rotates counterclockwise at a constant rate. You can use one of the wheel's spokes to measure the wheel's angular displacement, theta. How is this angular displacement related to the radius of the wheel, r, and the arc length, s, along the circumference of the wheel?
theta = s/r