Question 1

In the figure, a 10-lb weight is suspended from two spring scales, each of which has negligible weight. Which one of the following statements about the readings in the scales is true? 
A) Each scale will read 5 lb.
B) The lower scale will read zero, the top scale will read 10 lb.
C) Each scale will show a reading between one and 10 lb, such that the sum of the two is 10 lb. However, exact readings cannot be determined without more information.
D) The top scale will read zero, the lower scale will read 10 lb.
E) None of these is true.

Accepted Answer

The answer of In the figure, a 10-lb weight is...

Question 2

Two blocks, A and B, are being pulled to the right along a horizontal surface by a horizontal 100-N pull, as shown in the figure. Both of them are moving together at a constant velocity of 2.0 m/s to
The right, and both weigh the same.  Which of the figures below shows a correct free-body diagram of the horizontal forces acting on
The lower block, B? 
A) 
B) 
C) 
D) 
E) None of these diagrams is correct.

Accepted Answer

The answer of Two blocks, A and B, are being...

Question 3

A person who normally weighs 700 N is riding in a rather swift elevator that is moving at a constant speed of 9.8 m/s. If this person is standing on a bathroom scale inside the elevator, what
Would the scale read?
A) 700 N
B) more than 700 N
C) less than 700 N
D) It could be more or less than 700 N, depending on whether the elevator is going up or down.

Accepted Answer

When the elevator moves at a constant speed, there is no acceleration, so the person's weight appears the same as it would if they were standing still. The scale reads the normal force, which equals the gravitational force (weight) in this scenario.

Question 4

A fireman is sliding down a fire pole. As he speeds up, he tightens his grip on the pole, thus increasing the vertical frictional force that the pole exerts on the fireman. When the force on his
Hands equals his weight, what happens to the fireman?
A) The fireman comes to a stop.
B) The fireman descends with a smaller but non-zero acceleration.
C) The fireman descends with slower and slower speed.
D) The acceleration of the fireman is now upward.
E) The fireman continues to descend, but with constant speed.

Accepted Answer

When the vertical frictional force equals the fireman's weight, the net force acting on the fireman becomes zero. According to Newton's second law, when the net force is zero, the acceleration is also zero. Therefore, the fireman continues to move downward at a constant speed, not accelerating.

Question 5

An object of mass  m  rests on a flat table. The earth pulls on this object with a force of magnitude  mg . What is the reaction force to this pull?
A) The table pushing up on the object with force  mg .
B) The table pushing down on the floor with force  mg . 
C) The object pushing down on the table with force  mg .
D) The table pulling upward on the Earth with force  mg .
E) The object pulling upward on the Earth with force  mg .

Accepted Answer

According to Newton's third law, every action has an equal and opposite reaction. The Earth pulls the object downward with a force of mg, so the object pulls upward on the Earth with an equal force of mg.

Question 6

You are standing in a moving bus, facing forward, when you suddenly slide forward as the bus comes to an immediate stop. What force caused you to slide forward?
A) the force due to friction between you and the floor of the bus
B) the normal force due to your contact with the floor of the bus
C) gravity
D) There is not a force causing you to slide forward.

Accepted Answer

When the bus comes to an immediate stop, you slide forward not because of an external force acting in the direction of your motion, but due to your own inertia. Your body tends to maintain its state of motion (Newton's first law of motion), and no external horizontal force is applied to you to cause the sliding. The options A, B, and C describe forces that act in different contexts and do not directly cause the sliding forward motion when the bus stops.

Question 7

A person is using a rope to lower a 5.0-N bucket into a well with a constant speed of 2.0 m/s. What is the magnitude of the force exerted by the rope on the bucket?
A) 0.00 N
B) 5.0 N
C) 10 N
D) 2.0 N
E) 49 N

Accepted Answer

Since the bucket is moving at a constant speed, the net force acting on it is zero. This means the force exerted by the rope must exactly balance the weight of the bucket, which is 5.0 N.

Question 8

A person who normally weighs 700 N is riding in an elevator that is moving upward but slowing down at a steady rate. If this person is standing on a bathroom scale inside the elevator, what
Would the scale read?
A) 700 N
B) less than 700 N
C) more than 700 N
D) It could be more or less than 700 N, depending on whether the magnitude of the acceleration is greater than or less than 9.8 m/s².

Accepted Answer

When the elevator is moving upward but slowing down, it is decelerating in the upward direction, which means the acceleration is downward. This situation makes the apparent weight (what the scale reads) less than the actual weight because the net acceleration reduces the normal force exerted by the scale on the person.

Question 9

The figure shows two boxes, with $m 1 > m 2$ that are on a level frictionless surface. We can apply a horizontal force $\overrightarrow { \mathrm { F} }$  either toward the right on $m 1$ or toward the left on $m _ { 2 }$ The magnitude of the force that the boxes exert on each other is

A) larger if $\overrightarrow { \mathbf { F } }$ is applied toward the left.
B) the same in either case.
C) larger if $\overrightarrow { \mathbf { F } }$ is applied toward the right.
D) zero newtons in either case.

Accepted Answer

The answer of The figure shows two boxes, with \(m...

Question 10

Inside of a train a ball of weight W is hanging by a light wire at rest from the ceiling. The wire makes an angle θ with the ceiling, as shown in the figure. Which one of the following conditions
Must be true about the tension T in the wire?

A) $T \tan \theta = W$
B) $T \cos \theta = W$
C) T = W
D) T = ma
E) $T \sin \theta = W$

Accepted Answer

The answer of Inside of a train a ball of...

Question 11

Two blocks, A and B, are being pulled to the right along a horizontal surface by a horizontal 100-N pull, as shown in the figure. Both of them are moving together at a constant velocity of 2.0 m/s to
The right, and both weigh the same.  Which of the figures below shows a correct free-body diagram of the horizontal forces acting on
The upper block, A? 
A) 
B)
(No horizontal forces act on $A$.) 
C)$A \longrightarrow 50 \mathrm {~N}$ 
D)$\mathrm{A} \longrightarrow 100 \mathrm{~N}$ 
E)

Accepted Answer

The answer of Two blocks, A and B, are being...

Question 12

A horse pulls a cart with force $\vec { F }$ As a result of this force the cart accelerates with constant acceleration. The magnitude of the force that the cart exerts on the horse
A) less than the magnitude of $\overrightarrow { \mathrm { F } }$
B) is zero newtons.
C) greater than the magnitude of $\vec { F }$
D) equal to the magnitude of $\overrightarrow { \mathrm { F } }$
E) cannot be determined without knowing the mass of the horse.

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force that the cart exerts on the horse is equal in magnitude and opposite in direction to the force $\vec { F }$ that the horse exerts on the cart.

Question 13

A push of magnitude  P  acts on a box of weight  W  as shown in the figure. The push is directed at an angle  $\theta$ below the horizontal, and the box remains a rest. The box rests on a horizontal surface that has some friction with the box. The normal force on the box due to the floor is equal to

A)  W+P .
B)  W .
C) $W - P \sin \theta$
D) $W + P \cos \theta$
E) $W + P \sin \theta$

Accepted Answer

The answer of A push of magnitude  P ...

Question 14

A golf club hits a golf ball with a force of 2400 N, sending the ball into the air. The force exerted on the club by the ball must be less than 2400 N or else the ball would not have moved forward.
A) True 
B) False 
C) The answer depends on whether the golfer followed through with the swing.

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force exerted on the club by the ball is exactly 2400 N, not less.

Question 15

When a 45-kg person steps on a scale in an elevator, the scale reads a steady 410 N. Which of the following statements must be true? (There could be more than one correct choice.)
A) The elevator is accelerating downward at a constant rate.
B) The elevator is moving downward at a constant rate.
C) The elevator is accelerating upward at a constant rate.
D) The elevator is moving upward at a constant rate.
E) From the given information, we cannot tell if the elevator is moving up or down.

Accepted Answer

The scale reading is less than the person's weight, so the elevator must be accelerating downward or moving downward at a constant rate. We cannot tell from the given information whether the elevator is accelerating or moving at a constant rate.

Question 16

An object of weight W is in freefall close to the surface of Earth. The magnitude of the force that the object exerts on Earth is
A) cannot be determined without knowing the relative masses of the object and the earth.
B) equal to W.
C) less than W.
D) greater than W.
E) zero.

Accepted Answer

According to Newton's third law of motion, every action has an equal and opposite reaction. Therefore, if an object of weight W is in freefall, it exerts a force on Earth equal to its weight (W), just as Earth exerts a gravitational force on the object equal to its weight.

Question 17

The acceleration due to gravity is lower on the Moon than on Earth. Which one of the following statements is true about the mass and weight of an astronaut on the Moon's surface, compared to
Earth?
A) Both mass and weight are the same.
B) Both mass and weight are less.
C) Mass is less, weight is the same.
D) Mass is the same, weight is less.

Accepted Answer

Mass is a measure of the amount of matter in an object and does not change with location. Weight is the force exerted by gravity on an object and varies with the strength of the gravitational field. Since the Moon's gravitational pull is weaker than Earth's, an astronaut's weight is less on the Moon, but their mass remains unchanged.

Question 18

As shown in the figure, a woman is straining to lift a large crate, but without success because it is too heavy. We denote the forces on the crate as follows: P is the magnitude of the upward force
Being exerted on the crate by the person, C is the magnitude of the vertical contact force on the
Crate by the floor, and W is the weight of the crate. How are the magnitudes of these forces related
While the person is trying unsuccessfully to lift the crate?

A) P + C > W
B) P + C < W
C) P + C = W
D) P = C

Accepted Answer

The answer of As shown in the figure, a woman...

Question 19

A 75-N box rests on a perfectly smooth horizontal surface. The minimum force need to start the box moving is
A) 75 N.
B) 750 N.
C) 7.5 N.
D) any horizontal force greater than zero.

Accepted Answer

Since the surface is perfectly smooth, there is no friction. Therefore, any horizontal force greater than zero will start the box moving.

Question 20

When a 45-kg person steps on a scale in an elevator, the scale reads a steady 480 N. Which of the following statements must be true? (There could be more than one correct choice.)
A) The elevator is moving downward at a constant rate.
B) The elevator is moving upward at a constant rate.
C) The elevator is accelerating downward at a constant rate.
D) The elevator is accelerating upward at a constant rate.
E) From the given information, we cannot tell if the elevator is moving up or down.

Accepted Answer

The answer of When a 45-kg person steps on a...

Quiz 4: Dynamics: Newtons Laws of Motion

In the figure, a 10-lb weight is suspended from two spring scales, each of which has negligible weight. Which one of the following statements about the readings in the scales is true?

A person who normally weighs 700 N is riding in a rather swift elevator that is moving at a constant speed of 9.8 m/s. If this person is standing on a bathroom scale inside the elevator, what Would the scale read?

A fireman is sliding down a fire pole. As he speeds up, he tightens his grip on the pole, thus increasing the vertical frictional force that the pole exerts on the fireman. When the force on his Hands equals his weight, what happens to the fireman?

An object of mass m rests on a flat table. The earth pulls on this object with a force of magnitude mg . What is the reaction force to this pull?

You are standing in a moving bus, facing forward, when you suddenly slide forward as the bus comes to an immediate stop. What force caused you to slide forward?

A person is using a rope to lower a 5.0-N bucket into a well with a constant speed of 2.0 m/s. What is the magnitude of the force exerted by the rope on the bucket?

A person who normally weighs 700 N is riding in an elevator that is moving upward but slowing down at a steady rate. If this person is standing on a bathroom scale inside the elevator, what Would the scale read?

Inside of a train a ball of weight W is hanging by a light wire at rest from the ceiling. The wire makes an angle θ with the ceiling, as shown in the figure. Which one of the following conditions Must be true about the tension T in the wire?

A horse pulls a cart with force F⃗\vec { F }F As a result of this force the cart accelerates with constant acceleration. The magnitude of the force that the cart exerts on the horse

A push of magnitude P acts on a box of weight W as shown in the figure. The push is directed at an angle θ\thetaθ below the horizontal, and the box remains a rest. The box rests on a horizontal surface that has some friction with the box. The normal force on the box due to the floor is equal to

A golf club hits a golf ball with a force of 2400 N, sending the ball into the air. The force exerted on the club by the ball must be less than 2400 N or else the ball would not have moved forward.

When a 45-kg person steps on a scale in an elevator, the scale reads a steady 410 N. Which of the following statements must be true? (There could be more than one correct choice.)

An object of weight W is in freefall close to the surface of Earth. The magnitude of the force that the object exerts on Earth is

The acceleration due to gravity is lower on the Moon than on Earth. Which one of the following statements is true about the mass and weight of an astronaut on the Moon's surface, compared to Earth?

A 75-N box rests on a perfectly smooth horizontal surface. The minimum force need to start the box moving is

When a 45-kg person steps on a scale in an elevator, the scale reads a steady 480 N. Which of the following statements must be true? (There could be more than one correct choice.)

A horse pulls a cart with force $\vec { F }$ As a result of this force the cart accelerates with constant acceleration. The magnitude of the force that the cart exerts on the horse