Question 1

A dog is standing in the bed of a pickup truck. The bed is coated with ice, causing the force of friction between the dog and the truck to be zero. The truck is initially at rest, and then accelerates to the right, moving along a flat road. As seen from a stationary observer (watching the truck move to the right), the dog
A) does not move left or right, but the back of the truck moves towards the dog.
B) moves to the right, but not as quickly as the truck is moving to the right, causing it to slide towards the back of the truck.
C) moves to the right at the same rate as the truck, so it doesn't slide.
D) moves to the left, as the truck moves to the right, causing the dog to slide towards the back of the truck.

Accepted Answer

Since there is no friction between the dog and the truck bed, the dog remains stationary relative to the ground as the truck accelerates to the right. This makes it appear as if the back of the truck moves towards the dog from the perspective of a stationary observer.

Question 2

An 1100-kg car traveling at 27.0 m/s starts to slow down and comes to a complete stop in 578 m. What is the magnitude of the average braking force acting on the car?
A) 690 N
B) 550 N
C) 410 N
D) 340 N

Accepted Answer

The work done by the braking force is equal to the initial kinetic energy of the car. Using the equation for kinetic energy, KE = (1/2)mv^2, the initial kinetic energy of the car is (1/2)(1100 kg)(27.0 m/s)^2 = 404,100 J.

The work done by the braking force can also be expressed as the product of the braking force and the distance over which the force acts. Therefore, the magnitude of the average braking force can be calculated using the equation F = W/d, where W is the work done by the braking force and d is the distance over which the force acts.

Substituting the values given in the problem, F = 404,100 J / 578 m = 698.61 N, which rounds to 690 N. Therefore, the answer is choice A, 690 N.

Question 3

Point P in the figure indicates the position of an object traveling at constant speed clockwise around the circle. Which arrow best represent the direction the object would travel if the net external force on it were suddenly reduced to zero? 
A) 
B) 
C) 
D) 
E)

Accepted Answer

D

Question 4

A stalled car is being pushed up a hill at constant velocity by three people. The net force on the car is
A) zero.
B) up the hill and equal to the weight of the car.
C) down the hill and equal to the weight of the car.
D) up the hill and greater than the weight of the car.
E) down the hill and greater than the weight of the car.

Accepted Answer

Since the car is being pushed at a constant velocity, the forces acting on it are balanced. The force exerted by the three people pushing the car up the hill is equal and opposite to the force of friction acting on the car, resulting in a net force of zero. Therefore, choice A is the correct answer.

Question 5

If a 5.0 kg box is pulled simultaneously by a 10.0 N force and a 5.0 N force, then its acceleration must be A) 3.0 m/s². B) 2.2 m/s². C) 1.0 m/s². D) We cannot tell from the information given.

Accepted Answer

The answer of If a 5.0 kg box is pulled...

Question 6

Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest
A) right after the object is released.
B) at the top of its trajectory.
C) The acceleration of the object is the same throughout the entire trajectory.

Accepted Answer

The force of air drag is proportional to the speed of the object, and since the object is being thrown upward, its velocity is initially increasing. Therefore, the force of air drag is also increasing in magnitude, causing the acceleration to be greatest right after the object is released. As the object continues to rise, its speed decreases, and so does the force of air drag, causing the acceleration to decrease as well.

Question 7

A woman is straining to lift a large crate, without success because it is too heavy. We denote the forces on the crate as follows: P is the upward force the woman exerts on the crate, C is the vertical contact force exerted on the crate by the floor, and W is the weight of the crate. How are the magnitudes of these forces related while the woman is trying unsuccessfully to lift the crate?
A) P + C = W
B) P + C < W
C) P + C > W
D) P = C

Accepted Answer

P + C = W. When the woman is trying to lift the crate but is unsuccessful, the crate does not move, indicating it is in static equilibrium. Therefore, the sum of the upward forces (P + C) must equal the downward force (W) due to gravity.

Question 8

An object is moving forward with a constant velocity. Which statement about this object MUST be true?
A) The net force on the object is zero.
B) The net force on the object is in the forward direction.
C) No forces are acting on the object.
D) The acceleration of the object is in the forward direction.

Accepted Answer

If the object is moving forward with constant velocity, its acceleration is zero. According to Newton's Second Law, the net force on an object is equal to its mass multiplied by its acceleration. Since the acceleration is zero, the net force must also be zero. Therefore, choice A is the correct statement. Choices B and D are not necessarily true because there can still be forces acting on the object, as long as they all balance out to create zero net force. Choice C is not necessarily true because if there were no forces acting on the object, it would either be at rest or moving with constant velocity but not necessarily forward.

Question 9

A car is being towed at constant velocity on a horizontal road using a horizontal chain. The tension in the chain must be equal to the weight of the car in order to maintain constant velocity.

Accepted Answer

The tension in the chain must balance the frictional forces opposing the car's motion, not its weight, to maintain constant velocity. The weight of the car is counteracted by the normal force from the road.

Question 10

A ball is tossed vertically upward. When it reaches its highest point (before falling back downward)
A) the velocity is zero, the acceleration is directed downward, and the force of gravity acting on the ball is directed downward.
B) the velocity is zero, the acceleration is zero, and the force of gravity acting on the ball is zero.
C) the velocity is zero, the acceleration is zero, and the force of gravity acting on the ball is directed downward.
D) the velocity and acceleration reverse direction, but the force of gravity on the ball remains downward.
E) the velocity, acceleration, and the force of gravity on the ball all reverse direction.

Accepted Answer

At the highest point of its trajectory, a ball's velocity is zero because it stops for an instant before falling back down. However, acceleration due to gravity remains directed downward at approximately 9.8 m/s^2, and the force of gravity also continues to act downward on the ball. This is because gravity is a constant force acting on objects near Earth's surface, influencing their acceleration regardless of their momentary state of motion.

Question 11

Suppose you are playing hockey on a new-age ice surface for which there is no friction between the ice and the hockey puck. You wind up and hit the puck as hard as you can. After the puck loses contact with your stick, the puck will
A) start to slow down.
B) not slow down or speed up.
C) speed up a little, and then slow down.
D) speed up a little, and then move at a constant speed.

Accepted Answer

Without friction, there are no forces acting on the puck to slow it down or speed it up. Therefore, it will continue to move at a constant speed in a straight line until it is acted upon by another force.

Question 12

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward but is gradually slowing down at a rate of 9 m/s²? _f is the force of the floor on the person and _g is the force of gravity on the person. A) B) C) D) E)

Accepted Answer

The answer of Which one of the following free-body diagrams...

Question 13

A 7.0-kg object is acted on by two forces. One of the forces is 10.0 N acting toward the east. Which of the following forces is the other force if the acceleration of the object is 1.0 m/s² toward the east? A) 6.0 N east B) 3.0 N west C) 12 N east D) 9.0 N west E) 7.0 N west

Accepted Answer

The answer of A 7.0-kg object is acted on by...

Question 14

You are seated in a bus and notice that a hand strap that is hanging from the ceiling hangs away from the vertical in the backward direction. From this observation, you can conclude that
A) the velocity of the bus is forward.
B) the velocity of the bus is backward.
C) You cannot conclude anything about the direction of the velocity of the bus.

Accepted Answer

The answer of You are seated in a bus and...

Question 15

A 615 N student standing on a scale in an elevator notices that the scale reads 645 N. From this information, the student knows that the elevator must be moving
A) downward.
B) upward.
C) You cannot tell if it is moving upward or downward.

Accepted Answer

The answer of A 615 N student standing on a...

Question 16

An object is moving to the right, and experiencing a net force that is directed to the right. The magnitude of the force is decreasing with time. The speed of the object is
A) increasing.
B) decreasing.
C) constant in time.

Accepted Answer

If the net force is in the same direction as the object's motion and is decreasing, then the object's acceleration is also decreasing. However, as long as the net force is greater than the frictional or other resisting forces, there will still be an acceleration, which means the velocity (and therefore speed) will continue to increase. Therefore, the correct answer is A) increasing.

Question 17

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point down the ramp.

Accepted Answer

Since the crate is sliding down the ramp at a constant speed, the net force on the crate must be zero (balanced forces). Therefore, the vector sum of all the forces acting on the crate must be zero and not necessarily point down the ramp.

Question 18

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? _f is the force of the floor on the person and _g is the force of gravity on the person. A) B) C) D) E)

Accepted Answer

Since the elevator is traveling upward with a constant velocity, the net force on the person must be zero. This means that the upward force from the floor (_f) must be equal in magnitude to the downward force of gravity (_g). Therefore, the free-body diagram should show those two forces as equal in magnitude and opposite in direction. Choice B is the only diagram that accurately represents this situation.

Question 19

You are standing in a moving bus, facing forward, and you suddenly fall forward as the bus comes to an immediate stop. The force acting on you that causes you to fall forward is
A) the force of gravity.
B) the normal force due to your contact with the floor of the bus.
C) the force due to static friction between you and the floor of the bus.
D) the force due to kinetic friction between you and the floor of the bus.
E) No forces were acting on you to cause you to fall.

Accepted Answer

When the bus comes to an immediate stop, your body tends to continue moving forward due to inertia, not because of any external force acting on you in the forward direction. This is an example of Newton's first law of motion, which states that an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced external force. In this scenario, no external forward force is acting on you; you fall forward because the bus stops moving and your body tries to maintain its state of motion.

Question 20

The figure shows an acceleration-versus-force graph for three objects pulled by rubber bands. The mass of object 2 is 36 kg. What are the masses of objects 1 and 3? 
A) 14 kg and 90 kg
B) 72 kg and 18 kg
C) 90 kg and 18 kg
D) 14 kg and 72 kg

Accepted Answer

The answer of The figure shows an acceleration-versus-force graph for...

Quiz 5: Force and Motion

An 1100-kg car traveling at 27.0 m/s starts to slow down and comes to a complete stop in 578 m. What is the magnitude of the average braking force acting on the car?

Point P in the figure indicates the position of an object traveling at constant speed clockwise around the circle. Which arrow best represent the direction the object would travel if the net external force on it were suddenly reduced to zero?

A stalled car is being pushed up a hill at constant velocity by three people. The net force on the car is

If a 5.0 kg box is pulled simultaneously by a 10.0 N force and a 5.0 N force, then its acceleration must be

Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest

An object is moving forward with a constant velocity. Which statement about this object MUST be true?

A car is being towed at constant velocity on a horizontal road using a horizontal chain. The tension in the chain must be equal to the weight of the car in order to maintain constant velocity.

A ball is tossed vertically upward. When it reaches its highest point (before falling back downward)

Suppose you are playing hockey on a new-age ice surface for which there is no friction between the ice and the hockey puck. You wind up and hit the puck as hard as you can. After the puck loses contact with your stick, the puck will

A 7.0-kg object is acted on by two forces. One of the forces is 10.0 N acting toward the east. Which of the following forces is the other force if the acceleration of the object is 1.0 m/s2 toward the east?

You are seated in a bus and notice that a hand strap that is hanging from the ceiling hangs away from the vertical in the backward direction. From this observation, you can conclude that

A 615 N student standing on a scale in an elevator notices that the scale reads 645 N. From this information, the student knows that the elevator must be moving

An object is moving to the right, and experiencing a net force that is directed to the right. The magnitude of the force is decreasing with time. The speed of the object is

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point down the ramp.

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? f is the force of the floor on the person and g is the force of gravity on the person.

You are standing in a moving bus, facing forward, and you suddenly fall forward as the bus comes to an immediate stop. The force acting on you that causes you to fall forward is

The figure shows an acceleration-versus-force graph for three objects pulled by rubber bands. The mass of object 2 is 36 kg. What are the masses of objects 1 and 3?

A 7.0-kg object is acted on by two forces. One of the forces is 10.0 N acting toward the east. Which of the following forces is the other force if the acceleration of the object is 1.0 m/s² toward the east?

Which one of the following free-body diagrams best represents the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with an unchanging velocity? _f is the force of the floor on the person and _g is the force of gravity on the person.