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

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

D

Question 3

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

C

Question 4

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 5

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

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

Question 6

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

The fact that the car is being pushed up the hill at constant velocity means that the net force on the car is zero. If the net force were greater than zero, the car would be accelerating either up or down the hill. The weight of the car is balanced by the force of the three people pushing it up the hill, resulting in a net force of zero.

Question 7

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 8

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 magnitude of the average braking force can be found using the work-energy principle. The work done by the braking force is equal to the change in kinetic energy of the car. The initial kinetic energy (KE) of the car is $ \frac{1}{2}mv^2 $, where $ m = 1100 \, \text{kg} $ is the mass of the car and $ v = 27.0 \, \text{m/s} $ is its initial velocity. The final kinetic energy is 0 (since the car comes to a stop). Thus, the change in kinetic energy is $ \Delta KE = 0 - \frac{1}{2} \cdot 1100 \cdot 27.0^2 $.The work done by the braking force is also given by $ W = F \cdot d $, where $ F $ is the average braking force and $ d = 578 \, \text{m} $ is the distance over which the force is applied. Setting the work equal to the change in kinetic energy gives $ F \cdot 578 = -\frac{1}{2} \cdot 1100 \cdot 27.0^2 $.Solving for $ F $ gives $ F = -\frac{\frac{1}{2} \cdot 1100 \cdot 27.0^2}{578} \approx -690 \, \text{N} $. The negative sign indicates that the force is in the opposite direction of the car's initial motion, which is expected for a braking force. The magnitude of this force is 690 N.

Question 9

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

The answer of Point P in the figure indicates the...

Question 10

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 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, the puck will continue to move at a constant speed in the direction of the force applied (from the stick's hit). There will be no external forces to slow it down or speed it up. Therefore, the answer is B) not slow down or speed up.

Question 12

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 with a constant velocity, it means that there is no net force acting on it. If there was a net force, the object would either accelerate or decelerate, changing its velocity. Therefore, choice A is the correct answer.

Question 13

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 14

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) True
B) False

Accepted Answer

The tension in the chain must be equal to the frictional force opposing the motion, not the weight of the car, to maintain constant velocity.

Question 15

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 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

The object is experiencing a net force to the right, which means there is an acceleration to the right. Since the net force is decreasing with time, the acceleration is also decreasing with time. However, as long as the acceleration is positive, the speed must be increasing. Therefore, the answer is A, increasing.

Question 17

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 18

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...

Question 19

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

Right after the object is released, it has its maximum initial speed. As the object moves upward, the force of air drag acts in the direction opposite the velocity. This drag force reduces the acceleration of the object. The acceleration of the object decreases until it reaches the maximum height at the top of the trajectory where its speed is zero. From there, the object starts to fall back down, and the acceleration increases again due to the force of gravity. However, initially, the drag force is still acting in the opposite direction of the motion, so the acceleration is the greatest right after the object is released.

Question 20

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.
A) True
B) False

Accepted Answer

If the crate is sliding at a constant speed, the net force acting on it is zero, meaning the vector sum of all forces is zero, not pointing down the ramp.

Quiz 5: Force and Motion

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

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

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

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 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 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?

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

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.

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

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

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?

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 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.

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?