Deck 4: Why Things Move As They Do

Question 1

A stationary firecracker explodes, breaking into two parts of equal mass. One part is moving north at 20 m/s. The velocity of the other part is

A) 20 m/s with a direction that's impossible to predict without more information.
B) also northward at 20 m/s.
C) zero.
D) southward at 20 m/s.
E) impossible to predict without more information.

Answer 1

southward at 20 m/s.

Question 2

An auto moves at a steady 50 mph down a straight level road. The direction of the force of air resistance on the car is

A) sideways.
B) downward.
C) backward.
D) zero.
E) forward.

Answer 2

backward.

Question 3

A pool ball moving at 3 m/s collides head- on with an identical pool ball that's initially at rest. Just after the collision, the second ball moves away at 2 m/s while the first ball

A) moves at 3 m/s in a direction opposite to the second ball.
B) moves at 1 m/s in the same direction as the second ball.
C) is at rest.
D) continues moving at 3 m/s in the same direction.
E) moves at 1 m/s in a direction opposite to the second ball.

Answer 3

moves at 1 m/s in the same direction as the second ball.

Question 4

Are there any kinds of situations in which the momentum of a moving system is not conserved?

A) No, because the momentum of any system is always conserved.
B) Yes, if there is friction acting between different parts of the system.
C) Yes, if some of the parts of the system collide with each other.
D) Yes, if any part of the system is acted upon by forces external to the system.
E) No, because the law of inertia demands that any moving system must keep moving.

Question 5

An auto travels down a straight, level road at constant speed. One force that acts on the auto is

A) gravity pushing upward on the auto.
B) the road pushing upward on the auto.
C) the auto pushing downward on the road.
D) the road pulling downward on the auto.
E) None of the above.

Question 6

One force acting on your body right now is your weight. Which of the following is the best description of the other member of the "force pair" [of which your weight is one member]?

A) The force by the surface of the seat pushing upward on your body.
B) The force by your body pushing downward on the seat.
C) The gravitational force by your body pushing downward on Earth.
D) The gravitational force by your body pulling upward on Earth.
E) The force by Earth pulling downward on your body.

Question 7

The main point of Newton's law of motion is that forces cause

A) energy.
B) acceleration.
C) velocity.
D) All of the above.
E) None of the above.

Question 8

The "drive force" that pushes a car forward is

A) the push of the road against the drive tires.
B) the force of the expanding gases inside the engine.
C) the push of the drive tires against the road.
D) the force of the engine turning the drive tires.
E) unknown to science.

Question 9

Any rock having a very large mass would necessarily

A) move very slowly.
B) have a very large weight.
C) be very difficult to accelerate.
D) All of the above.
E) need to go on a diet.

Question 10

Is any force exerted on you when you slow down while moving along a straight line?

A) No, no force acts as long as you are slowing down.
B) Yes, there is a backward force on you, opposite to your direction of motion.
C) Yes, there is a sideways force on you.
D) Yes, there is a force on you but it is impossible to state the direction of this force because the question contains insufficient information.
E) Yes, there is a forward force on you, along your direction of motion.

Question 11

One newton is about equal to

A) 1/4 pound.
B) 1/10 kilogram.
C) 1/4 kilogram.
D) 4 pounds.
E) 4 kilograms.

Question 12

Would you be richer if you had a hunk of gold whose weight is 1 newton on the moon, or one whose weight is 1 newton on Earth, and why?

A) 1 newton on the moon, because then the gold's weight on the moon would be larger.
B) 1 newton on Earth, because then the gold's mass would be larger.
C) 1 newton on Earth, because then the gold's weight on Earth would be larger.
D) 1 newton on the moon, because then the gold's mass would be larger.
E) It wouldn't make any difference, because the amount of actual gold would be the same in both cases.

Question 13

Regarding the relation between acceleration, force, and mass, an object's acceleration is

A) inversely proportional to the force on it and inversely proportional to the object's mass.
B) inversely proportional to the force on it and proportional to the object's mass.
C) proportional to the inverse of the height of the Empire State Building.
D) proportional to the force on it and proportional to the object's mass.
E) proportional to the force on it and inversely proportional to the object's mass.

Question 14

Suppose that we wish to find the "net force" on an automobile, in order to apply Newton's law of motion to the motion of the automobile. As part of the net force, do we need to include "internal frictional forces" due to internal gears, bearings, etc.?

A) Yes, because every internal and external force must be included.
B) No, because only external forces need to be included.
C) Yes, because of Newton's law of force pairs.
D) Yes, because these forces dissipate some of the car's energy.
E) No, because only the drive force needs to be included.

Question 15

You hold a 5- newton rock motionless in your hand. Regarding the forces on this rock,

A) there are no forces of any kind acting on the rock, because it is not moving.
B) the downward force of gravity is balanced by the upward force of air resistance.
C) the net force on the rock is 5 newtons, directed upward.
D) the net force on the rock is 5 newtons, directed downward.
E) the net force on the rock is zero.

Question 16

A book rests on a table, and the table rests on the ground. Which of the following pairs of forces forms a force pair, or action- reaction pair, obeying Newton's law of force pairs?

A) Gravity pulling down on the table and the book pushing down on the table.
B) Gravity pulling down on the book and the table pushing up on the book.
C) The table pushing up on the book and the book pushing down on the table.
D) Gravity pulling down on the book and the book pushing down on the table.
E) The ground pushing up on the table and the book pushing down on the table.

Question 17

You are in distant space, where there is no gravity. You hold two blocks of metal. They look and feel identical when touched, but you been informed that one is made of lightweight aluminum and the other of lead. Can you determine which one is lead without doing any kind of chemical analysis?

A) You can determine this by dropping them; the lead ball will fall fastest.
B) You can determine this, by tapping each block with your finger; the one that accelerates the most is aluminum.
C) You can determine this by dropping them; the aluminum ball will fall fastest.
D) You can determine this by giving each block a tap with your finger; the one that accelerates the most is the lead.
E) The above methods will not work.

Question 18

An object's "momentum" is defined as

A) its mass times its velocity.
B) its weight times its speed.
C) its force times its distance.
D) its mass times its speed.
E) its force time is velocity.

Question 19

Which of the following best describes the meaning of "force"?

A) A body exerts a force on another body when the first body causes the second body to accelerate.
B) The force of a moving body is the distance the body travels divided by the time it takes to travel that distance.
C) A body's force is the tendency of that body to continue moving once it is started moving.
D) The force that a body has is the amount of work that the body can do.
E) A force is a change in velocity.

Question 20

Consider the force by a baseball against a player's glove while the player is catching a fastball. The law of force pairs says that this force is one of a pair of forces. The other member of this pair is

A) the muscular force in the player's arms, i.e., the force by the player's muscles on the player's arm.
B) the player's grip on the glove, i.e., the force by the player's hand against the glove.
C) the frictional force by the ground on the player's shoes.
D) the weight of the ball.
E) the force by the glove on the ball.

Question 21

An apple weighing 3 newtons hangs, motionless, from a tree branch. What are the forces by the environment that act on this apple?

A) Only the upward lift of the branch.
B) the apple's weight and the branch's upward lift on the apple.
C) Only the apple's weight.
D) There are no forces by the environment on a motionless apple.
E) The apple's weight and the apple's downward pull on the branch.

Question 22

Marcia places a lead block and an iron block on the table, and hits both of them with the same force. The lead block is twice as massive as the iron block. The acceleration of the lead block is

A) a quarter of that of the iron block.
B) two times that of the iron block.
C) half that of the iron block.
D) equal to that of the iron block.
E) four times that of the iron block.

Question 23

A "force" could be best described as

A) something that a body possesses, that enables it to do work.
B) something that a body possesses, that enables it to keep moving.
C) something one body does to another body that can cause the second body to accelerate.
D) a mystical aura that emanates after midnight from physics laboratories.
E) something one body does to another body that keeps the second body moving.

Question 24

When you pull an object, such as a table, across the floor, the forward force by you on the table is equal but opposite to the backward force by the table on you. It seems as though these two forces should balance out, so that the table can't be moved. But the table does move, because

A) only one of these two forces actually acts on the table.
B) the force by you on the table is larger than the force of the table on you.
C) the floor pushes forward on the table.
D) the momentum always acts in a forward direction.
E) Newton's laws do not apply to the table considered as a separate object.

Question 25

An apple weighing 3 newtons hangs, motionless, from a tree branch. The net force on the apple is

A) impossible to determine from the information that is given.
B) 3 newtons downward.
C) 6 newtons downward.
D) 3 newtons upward.
E) None of the above.

Question 26

The basic physical principal principle that explains the operation of rocket engines is

A) the law of force pairs.
B) the law of inertia.
C) the atomic hypothesis.
D) Galileo's principle of falling.
E) Actually, rockets are unexplainable.

Question 27

The "drive force" that pushes a car forward is

A) actually zero whenever the car has no acceleration.
B) exerted by the engine pushing forward against the axle.
C) exerted by the road pushing upward against the tires.
D) exerted by the engine pushing backward against the axle.
E) exerted by the road pushing forward against the tires.

Question 28

You would be richest if your hunk of gold had a mass of one kilogram

A) on the moon.
B) on Earth.
C) Actually it wouldn't make any difference.

Question 29

An auto moves at a steady 50 mph down a straight level road. The net force on the auto is

A) zero.
B) sideways.
C) backward.
D) downward.
E) forward.

Question 30

Can two pool balls, both of them moving, have a total momentum of zero?

A) No, because any moving object has momentum.
B) No, because they both have energy.
C) Yes, if they are moving in opposite directions, both with the same speed.
D) Yes, if they are both moving outward from the same point.
E) Yes, but only at the instant that they collide.

Question 31

A car weighing 5000 N is traveling along a straight level road powered by a forward drive force of 500 N. The force of air resistance is 200 N, and rolling resistance is 100 N. The net force on the car is

A) zero.
B) 300 N backward.
C) 500 N forward.
D) 5000 N downward.
E) 200 N forward.

Question 32

Which of the following principles explains why guns recoil?

A) The law of inertia.
B) Conservation of momentum.
C) Newton's law of motion.
D) Conservation of energy.
E) None of the above.

Question 33

A one kilogram grapefruit weighs ten newtons. Suppose we take this grapefruit to the moon. The force of gravity on the grapefruit will then be

A) less than one kilogram.
B) ten newtons.
C) less than ten newtons.
D) one kilogram.
E) None of the above.

Question 34

It's harder to stop or turn a moving supertanker than a small speedboat because

A) the supertanker has a larger momentum.
B) the supertanker has a larger velocity.
C) the supertanker has more force.
D) the speed boat has a larger velocity.
E) the speedboat has more force.

Question 35

A certain grapefruit on Earth has a mass of one kilogram and a weight of one newton. When the grapefruit is on the moon its mass is

A) one kilogram.
B) less than ten newtons.
C) ten newtons.
D) less than one kilogram.

Question 36

One newton is about equal to

A) one- fourth kilogram.
B) four pounds.
C) one- fourth pound.
D) 10 m/sec².
E) one pound.

Question 37

Suppose that you are isolated and "floating" in outer space and that you hold a wooden block and a lead block, one in each hand, and that the two blocks look and feel identical. How could you tell which one is the lead block?

A) Give each one a light tap with your finger; the one that accelerates the most is the lead block.
B) Give each one a light tap with your finger; the one that accelerates the least is the lead block.
C) Let go of them; the one that falls the fastest is the lead block.
D) None of the above methods could tell you which block is the lead block.

Question 38

An auto weighing 3000 newtons has a forward drive force of 1000 newtons. Air resistance on the car is 100 newtons, and road resistance is 100 newtons. The auto moves along a straight level road. The net force on this auto is

A) 1000 newtons forward.
B) 1200 newtons forward.
C) 800 newtons backward.
D) 800 newtons forward.
E) 200 newtons backward.

Question 39

Mary pushes horizontally on a large, heavy table which is standing alone in the middle of a room, and notes that the table does not move despite the fact that she is pushing on it (see the figure). Why doesn't the table move?

A) Very massive objects, such as the table, are difficult to set into motion because of their large inertia.
B) The table pushes back on Mary with a force that is even larger than Mary's pushing force.
C) The force of gravity pulls downward on the table, and this force cancels the pushing force.
D) A frictional force is also exerted by the floor on the table, and this force is equal and opposite to the pushing force.
E) The table exerts a force on Mary, and this force is equal and opposite to the pushing force.

Question 40

A car weighing 5000 N is traveling along a straight level road powered by a forward drive force of 500 N. The force of air resistance is 200 N, and rolling resistance is 100 N. The car's acceleration is

A) in the forward direction.
B) zero.
C) in the backward direction.
D) in the downward direction.
E) in a direction that is sideways to the car.

Question 41

Jet planes operate by

A) magic.
B) sucking in air, heating it , and allowing it to expand out the back end of the engine.
C) rocket drive [i.e., ejecting heated rocket fuel rapidly out the back end of the engine].
D) sucking in air and blowing it rapidly out the back of the engine by means of propeller blades inside the engine.
E) ejecting ions out the back end of the engine.

Question 42

A girl lifts a ball by means of a string attached to the ball. The string exerts a 20 newton force on the ball. The ball weighs 8 newtons. The net force on the ball is

A) 8 newtons.
B) zero.
C) 28 newtons.
D) 12 newtons.
E) 20 newtons.

Question 43

A gold dealer has three blocks of solid gold. He informs you that the first block would weigh one pound on the very massive planet Jupiter, that the second block would weigh one pound on the moon, and that the third block would weigh one pound on Earth. Which block of gold would make you the richest? NOTE: On Jupiter, you would weigh nearly three times your normal weight.

A) Each of them would make you equally rich because they each contain the same amount of gold.
B) The third block.
C) The first block.
D) The second block.

Question 44

You hold a 2 newton apple, having a mass of 0.2 kg, at rest in your hand. The net force on the apple is then

A) 0.2 kg downward.
B) 0.2 kg upward.
C) zero.
D) 2 newtons downward.
E) 2 newtons upward.

Question 45

Forces of 8 N and 3 N act on an object. If the two forces act in opposite directions, the net force on the object is

A) 5 N.
B) 11 N.
C) zero.
D) 8 N.
E) impossible to determine.

Question 46

A small car and a large truck collide head- on. During the collision, the small car experiences

A) A much larger change in momentum than the truck.
B) A much larger acceleration than the truck.
C) A much larger force than the truck.
D) All of the above.
E) None of the above.

Question 47

An apple weighing 3 newtons hangs, motionless, from a tree branch. Newton's law of force pairs says that forces always come in pairs. One force acting on the apple is the apple's weight. What is the other force that forms a force pair with the weight?

A) The apple pulling downward on the branch.
B) Earth pulling downward on the apple.
C) The apple pulling upward on Earth.
D) The branch pulling upward on the apple.

Question 48

One force acting on a falling apple is the apple's weight. Which of the following is the best description of the other member of the "force pair" [of which the apple's weight is one member]?

A) The force of gravity by the apple pulling upward on Earth.
B) Air resistance acting upward on the apple.
C) The force of gravity by Earth pulling upward on the apple.
D) Gravity pulling downward on the apple.
E) The force of gravity by the apple pushing downward on Earth.

Question 49

A ball is thrown straight upward. While it is moving upward, the ball's acceleration is

A) in the downward direction.
B) in the horizontal direction.
C) in the upward direction.
D) zero, i.e., the ball is not accelerating.
E) None of the above.

Question 50

One- third as much net force is exerted on object A as on object B. The two objects have the same mass. How do their accelerations compare?

A) Object A has three times as much acceleration as object B.
B) Object A has one- sixth as much acceleration as object B.
C) Object A has one- third as much acceleration as object B.
D) They both have the same acceleration.
E) It is impossible to answer this without further information about the two objects.

Question 51

Suppose that you stand, motionless, on the floor. Regarding the force by the floor on your feet,

A) there is an downward force by the floor on your feet, even though you are not accelerating.
B) there is a downward force by the floor on your feet, and this force causes you to accelerate downwards.
C) as long as you remain motionless, there is no force by the floor on your feet.
D) there is an upward force by the floor on your feet, and this force causes you to accelerate upwards.
E) there is an upward force by the floor on your feet, even though you are not accelerating.

Question 52

If you went to the moon, you would find that

A) your mass would be reduced, but not your weight.
B) your weight would be increased.
C) it really is made of blue cheese.
D) your weight would be reduced, but not your mass.
E) both your weight and your mass would be reduced.

Question 53

Object A has twice as much mass as object B. If you exert the same force on these two objects, how do their accelerations compare?

A) Object A has four times as much acceleration as object B.
B) Object A has half as much acceleration as object B.
C) Object A has twice as much acceleration as object B.
D) They both have the same acceleration.
E) It is impossible to answer this without further details concerning the composition of the two object.

Question 54

A 39- kg girl standing at rest on slippery (frictionless) ice catches a 1- g ball moving at 10 m/s. Just afterward, the girl is

A) moving at 0.5 m/s.
B) moving at 2 m/s.
C) moving at 0.25 m/s.
D) moving at 4 m/s.
E) at rest.

Question 55

An auto moves at a steady 50 mph down a straight level road. Which of the following is the forward drive force on the auto?

A) The backward push by the engine on the car.
B) The backward push by the drive tires on the road.
C) The drive force is actually zero in this example, because the auto is moving at a constant speed in a straight line.
D) The forward push by the road on the tires.
E) The forward push by the engine on the car.

Question 56

You are in distant space. A giant boulder, many times larger than you, is at rest in front of you. You tap the boulder lightly with a small hammer. What does the boulder do?

A) It speeds up a little during the tap, but after the tap it soon [within a few minutes] slows down and comes to rest.
B) It accelerates during the tap, up to a slow speed [slower than walking speed], then keeps moving at that speed.
C) It remains at rest.
D) It accelerates both during and after the tap.
E) It accelerates during the tap, up to a high speed [faster than a fast- moving car], then keeps moving at that speed.

Question 57

A block of wood is given a brief push and then allowed to slide [without further pushing] along a table top, slowing down as it moves toward the east. As the block slides,

A) its acceleration is toward the east.
B) its acceleration is toward the west.
C) the net force on it is zero.
D) it has no acceleration.
E) its velocity is toward the west.

Question 58

You would be richest if your hunk of gold weighed 10 newtons

A) on Earth.
B) on the moon.
C) Actually it wouldn't make any difference.

Question 59

A ball is rolling along the floor. It is rolling toward the east, and slowing down as it rolls. As the ball rolls,

A) the net force on it is toward the west.
B) its velocity is toward the west.
C) Both of the above.
D) the net force on it is toward the east.
E) the net force on it is zero.

Question 60

You push your 2 kg physics book along a tabletop, pushing it with 10 newtons of force. The frictional force on it is 4 newtons. The book's acceleration is

A) 3 m/s².
B) 5 m/s².
C) 2 m/s².
D) zero.
E) 0.2 m/s².

Question 61

An auto weighing 3000 newtons has a forward drive force of 1000 newtons. Air resistance on the car is 100 newtons, and road resistance is 100 newtons. The auto moves along a straight level road. The force due to gravity acting on the auto is

A) 3000 newtons downward.
B) 3000 newtons upward.
C) zero.
D) 800 newtons upward.
E) 4200 newtons downward.

Question 62

Would it be easier [i.e., would it require less rocket fuel] to lift a rocket off the moon's surface or off Earth's surface, and why?

A) It would be equally difficult, because the rocket's mass would be the same on the moon as on Earth.
B) It would be impossible for the rocket to lift off of the moon, because there is no air on the moon.
C) It would be equally difficult, because the rocket's weight would be the same on the moon as on Earth.
D) It would be easier on the moon, because the rocket's weight would be less on the moon than it is on Earth.
E) It would be easier on the moon, because the rocket's mass would be less on the moon than it is on Earth.

Question 63

A 1 newton apple hangs from a tree branch. The force by the apple on Earth

A) cannot be determined from the given information, because the mass of the earth needs to be given.
B) is 1 newton downward.
C) is zero.
D) is 1 newton upward.
E) is much smaller than 1 newton, but not zero.

Question 64

Which of the following is the basic [and most accurate] meaning of "mass"? An object's "mass" is

A) the number of atoms it contains.
B) the amount of inertia it contains.
C) the amount [or quantity] of matter it contains.
D) the force exerted on it by gravity.

Question 65

The force needed to maintain a body at constant speed in outer space [far from all outside influences] is equal to

A) the force required to stop it.
B) the weight of the body.
C) zero.
D) the mass of the body.
E) None of the above.

Question 66

The law of inertia says that

A) if there is a force on a body, the body will have a changing acceleration.
B) if there is no force on a body, the body will have a changing velocity.
C) if there is a force on a body, the body will have an unchanging velocity.
D) if there is a force on a body, the body will have no acceleration.
E) if there is no force on a body, the body will have no acceleration.

Question 67

You push your 2 kg physics book along a tabletop, pushing it with 10 newtons of force. If the book is greased so that friction is negligible, the book's acceleration is

A) 5 m/s².
B) 20 m/s².
C) zero.
D) infinitely large.
E) 0.2 m/s².

Question 68

A girl lifts a ball by means of a string attached to the ball. The string exerts a 30 newton force on the ball. The ball weighs 20 newtons and has a mass of 2 kilograms. The acceleration of the ball is

A) 25 m/s².
B) 15 m/s².
C) 5 m/s².
D) zero.
E) 10 m/s².

Question 69

Suppose we subject a golf ball and a more massive lead ball to identical net forces. Then, compared to the golf ball, the lead ball must have

A) a larger acceleration.
B) a smaller acceleration.
C) a larger speed.
D) a smaller speed.
E) None of the above answers is necessarily true.

Question 70

You throw a ball straight upward. While it is moving upward, the net force on the ball is

A) zero.
B) in the downward direction.
C) in the horizontal direction.
D) in the upward direction.
E) directed oppositely to the acceleration.

Question 71

A rocket taking off straight upward develops a thrust of 10,000 newtons. The rocket weighs 2,000 newtons. The net force on the rocket, neglecting air resistance, is

A) 8,000 newtons.
B) 10,000 newtons.
C) 12, 000 newtons.
D) 2,000 newtons.
E) zero.

Question 72

Mary pushes horizontally on a large, heavy table, which is standing alone in the middle of a room, and notes that the table does not move despite the fact that she is pushing on it (see the figure). Why doesn't the table move?

A) The table had so much mass that its inertia kept it from moving.
B) Although it is true that forces cause accelerations, they do not cause velocities; therefore, the table acquired no velocity.
C) Newton's law of force pairs says that there is an opposite "reaction force" by the table against the instructor's hand, and this reaction force keeps the table from moving.
D) Frictional forces by the floor on the table legs acted in the opposite direction to produce a net force of zero.
E) According to Newton's meaning of the word "force," the horizontal push against the table was not really a force.