Question 1

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) Mass is less, weight is the same.
B) Mass is the same, weight is less.
C) Both mass and weight are less.
D) Both mass and weight are the same.

Accepted Answer

Mass is a measure of the amount of matter in an object, and it is not dependent on the gravitational field. Thus, the mass of an astronaut remains the same on the Moon as it is on Earth. Weight, on the other hand, is the force exerted on an object due to gravity, and it is dependent on the gravitational field. Since the gravitational acceleration is lower on the Moon than on Earth, the weight of an astronaut on the Moon's surface will be less than their weight on Earth. Therefore, choice B is correct, stating that the mass is the same, but the weight is less.

Question 2

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 object pushing down on the table with force mg.
C) The table pushing down on the floor with force mg.
D) The object pulling upward on the Earth with force mg.
E) The table pulling upward on the Earth with force mg.

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. When the Earth pulls on the object with a force of magnitude mg, the object pulls upward on the Earth with the same force magnitude, making choice D the correct answer.

Question 3

What is the mass of an object that experiences a gravitational force of 685 N near Earth's surface where g = 9.80 m/s²? A) 69.9 kg B) 68.5 kg C) 71.3 kg D) 72.7 kg

Accepted Answer

The mass of an object can be calculated using the formula F = mg, where F is the gravitational force, m is the mass, and g is the acceleration due to gravity. Rearranging the formula to solve for mass gives m = F/g. Substituting the given values, m = 685 N / 9.80 m/s^2 = 69.9 kg.

Question 4

An astronaut weighs 99 N on the Moon, where the acceleration of gravity is 1.62 m/s². How much does she weigh on Earth? A) 16 N B) 61 N C) 99 N D) 600 N E) 440 N

Accepted Answer

The astronaut's weight on Earth can be calculated using the ratio of the gravitational forces on Earth and the Moon. Since the acceleration due to gravity on Earth (9.8 m/s^2) is about 6 times that on the Moon (1.62 m/s^2), the astronaut's weight on Earth would be approximately 6 times her weight on the Moon. Therefore, 99 N * 6 ≈ 600 N.

Question 5

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

Newton's third law states that every action has an equal and opposite reaction. Therefore, the force exerted on the ball by the club is equal in magnitude to the force exerted on the club by the ball, but in the opposite direction. This means that the force exerted on the club by the ball is also 2400 N, making choice B the correct answer. The follow-through of the swing does not affect this principle.

Question 6

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) 7.5 N.
C) 750 N.
D) any horizontal force greater than zero.

Accepted Answer

Since the surface is perfectly smooth, implying no friction, any horizontal force greater than zero would be sufficient to start moving the box.

Question 7

If I weigh 741 N on Earth at a place where g = 9.80 m/s² and 5320 N on the surface of another planet, what is the acceleration due to gravity on that planet? A) 70.4 m/s² B) 51.4 m/s² C) 61.2 m/s² D) 81.0 m/s²

Accepted Answer

The answer of If I weigh 741 N on Earth...

Question 8

A net force of 125 N is applied to a certain object. As a result, the object accelerates with an acceleration of 24.0 m/s². The mass of the object is A) 3000 kg. B) 2880 kg. C) 144 kg. D) 0.200 kg. E) 5.21 kg.

Accepted Answer

Using Newton's second law of motion, $F = ma$, where $F$ is the force applied, $m$ is the mass of the object, and $a$ is the acceleration. Rearranging the formula to solve for mass, $m = \frac{F}{a}$. Substituting the given values, $m = \frac{125\,N}{24.0\,m/s^2} = 5.21\,kg$.

Question 9

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 upward at a constant rate.
B) The elevator is accelerating downward at a constant rate.
C) The elevator is moving upward at a constant rate.
D) 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...

Question 10

An object has a mass of 60 kg on Earth. What are the mass and weight of this object on the surface of the Moon where the acceleration due to gravity is only 1/6 of what it is on Earth?

Accepted Answer

The answer of An object has a mass of 60...

Question 11

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) greater than W.
B) less than W.
C) equal to W.
D) zero.
E) cannot be determined without knowing the relative masses of the object and the earth.

Accepted Answer

According to Newton's third law, for every action, there is an equal and opposite reaction. In this case, the force of gravity on the object is balanced by an equal and opposite force, which is the force that the object exerts on the Earth. Therefore, the magnitude of the force that the object exerts on the Earth is equal to its weight, which is W.

Question 12

A horse pulls a cart with force $\overrightarrow { \mathbf { F } }$ . 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) is zero newtons.
B) equal to the magnitude of $\overrightarrow { \mathbf { F } }$ .
C) less than the magnitude of $\overrightarrow { \mathbf { F } }$ .
D) greater than the magnitude of $\overrightarrow { \mathbf { F } }$ .
E) cannot be determined without knowing the mass of the horse.

Accepted Answer

According to Newton's third law, for every action, there is an equal and opposite reaction. So, the cart will exert a force on the horse equal in magnitude but opposite in direction to the force with which the horse pulls the cart. Therefore, the magnitude of the force that the cart exerts on the horse is equal to the magnitude of the force with which the horse pulls the cart, which is $\overrightarrow { \mathbf { F } }$.

Question 13

The figure shows two boxes, with m₁ > m₂, that are on a level frictionless surface. We can apply a horizontal force $\overrightarrow { \mathbf { F } }$ either toward the right on m₁ or toward the left on m₂. The magnitude of the force that the boxes exert on each other is A) zero newtons in either case. B) larger if $\overrightarrow { \mathbf { F } }$ is applied toward the right. C) larger if $\overrightarrow { \mathbf { F } }$ is applied toward the left. D) the same in either case.

Accepted Answer

Since m₁ > m₂, the box on the left has more mass than the box on the right. If we apply a force toward the left on the box with less mass (m₂), it will move to the left with an acceleration a. The force that the box with more mass (m₁) exerts on the other box will be equal and opposite to the force that we apply on m₂ according to Newton's Third Law. Thus, the force that the box with more mass exerts on the other box will be equal to F, the force that we apply on the box with less mass. The force of friction between the boxes will also be equal to F since the surface is frictionless. Therefore, the net force on the box with more mass will be F towards the right. Thus, according to Newton's Second Law, the acceleration of the box with more mass will be a' = F/m₁ = F/(m₂ + m₁). Since a' < a, the box with more mass will move to the right with a smaller acceleration. Therefore, the force that the boxes exert on each other will be larger if we apply the force toward the left on the box with less mass.

Question 14

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 sin θ = W
B) T cos θ = W
C) T tan θ = W
D) T = W
E) T = ma

Accepted Answer

The ball is at rest and therefore, the forces acting on the ball are balanced. The only two forces acting on the ball are its weight, W, acting downwards and the tension, T, acting upwards. These two forces are perpendicular to each other and therefore, we can resolve them into horizontal and vertical components. Let the angle between the tension and the ceiling be $	heta$.

The vertical component of tension is T sin $	heta$ which acts upwards and balances the weight W acting downwards. Therefore, T sin $	heta$ = W is the condition that must be true.

Question 15

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) 2.0 N
C) 5.0 N
D) 10 N
E) 49 N

Accepted Answer

When the bucket is being lowered with a constant speed, it means the net force acting on it is zero (because net force=mass x acceleration and the acceleration is zero). Therefore, the force exerted by the rope on the bucket must be equal and opposite to the weight of the bucket. The weight of the bucket is given as 5.0 N, so the magnitude of the force exerted by the rope on the bucket is also 5.0 N. Thus, the correct answer is C.

Question 16

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) more than 700 N B) less than 700 N C) 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

Since the elevator is slowing down, its acceleration is in the opposite direction of the person's weight, so the normal force (read by the scale) will be less than their weight. The exact reading will depend on the magnitude of the elevator's deceleration, which is not given.

Question 17

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) more than 700 N
B) less than 700 N
C) 700 N
D) It could be more or less than 700 N, depending on whether the elevator is going up or down.

Accepted Answer

Since the elevator is moving at a constant speed and not accelerating, there is no net force acting on the person. Therefore, the person's weight (and the reading on the scale) remains the same, which is 700 N.

Question 18

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 accelerating upward at a constant rate.
B) The elevator is accelerating downward at a constant rate.
C) The elevator is moving upward at a constant rate.
D) 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...

Question 19

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 slower and slower speed.
C) The fireman descends with a smaller but non-zero acceleration.
D) The fireman continues to descend, but with constant speed.
E) The acceleration of the fireman is now upward.

Accepted Answer

When the vertical frictional force equals the fireman's weight, the net force acting on the fireman in the vertical direction becomes zero. According to Newton's second law, when the net force is zero, the acceleration is also zero. This means the fireman will continue moving at whatever speed he has at that moment, without speeding up or slowing down, hence moving with constant speed.

Question 20

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) gravity
B) the normal force due to your contact with the floor of the bus
C) the force due to friction between you and the floor of the bus
D) There is not a force causing you to slide forward.

Accepted Answer

When the bus comes to an immediate stop, your body tends to remain in motion due to inertia, not because of an external force acting in the direction of motion. This is a consequence 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, there is no forward force being applied to you when you slide forward; instead, it's the lack of force to keep you stationary with the bus that causes you to slide forward.

Quiz 4: Forces and Newtons Laws of Motion

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?

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?

What is the mass of an object that experiences a gravitational force of 685 N near Earth's surface where g = 9.80 m/s2?

An astronaut weighs 99 N on the Moon, where the acceleration of gravity is 1.62 m/s2. How much does she weigh on Earth?

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

If I weigh 741 N on Earth at a place where g = 9.80 m/s2 and 5320 N on the surface of another planet, what is the acceleration due to gravity on that planet?

A net force of 125 N is applied to a certain object. As a result, the object accelerates with an acceleration of 24.0 m/s2. The mass of the object is

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 has a mass of 60 kg on Earth. What are the mass and weight of this object on the surface of the Moon where the acceleration due to gravity is only 1/6 of what it is on Earth?

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 horse pulls a cart with force F→\overrightarrow { \mathbf { 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

The figure shows two boxes, with m1 > m2, that are on a level frictionless surface. We can apply a horizontal force F→\overrightarrow { \mathbf { F } }F either toward the right on m1 or toward the left on m2. The magnitude of the force that the boxes exert on each other is

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 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?

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?

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 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?

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?

What is the mass of an object that experiences a gravitational force of 685 N near Earth's surface where g = 9.80 m/s²?

An astronaut weighs 99 N on the Moon, where the acceleration of gravity is 1.62 m/s². How much does she weigh on Earth?

If I weigh 741 N on Earth at a place where g = 9.80 m/s² and 5320 N on the surface of another planet, what is the acceleration due to gravity on that planet?

A net force of 125 N is applied to a certain object. As a result, the object accelerates with an acceleration of 24.0 m/s². The mass of the object is

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