Question 1

FIGURE 5-1 -In Figure 5-1, masses m₁ and m₂ are such that m₁ > m₂ and they lay on a level, frictionless surface. We can apply a horizontal force either from the left or from the right. The contact force between masses m₁ and m₂ is A) zero newtons. B) larger when is applied from the left. C) larger when is applied from the right. D) the same in either case. E) impossible to determine based on this data.

Accepted Answer

The answer of FIGURE 5-1 -In Figure 5-1, masses m₁...

Question 2

A locomotive is pulling a number of identical wagons along a level track and accelerating. Friction is negligible. Starting from the last wagon, the ratio of the forces between adjacent wagons is
A) 1:2:3:4 . . .
B) 1:2:4:8 . . .
C) 1:3:5:7 . . .
D)  . . .
E) 1:1:1:1 . . .

Accepted Answer

The answer of A locomotive is pulling a number of...

Question 3

A horse pulls a cart with force  . As a result of this force the cart accelerates with constant acceleration. What is the magnitude of the force that the cart exerts on the horse?
A) zero Newtons
B) equal to the magnitude of 
C) less than the magnitude of 
D) more than the magnitude of 
E) cannot be determined without additional information

Accepted Answer

According to Newton's Third Law, every action has an equal and opposite reaction. Therefore, the force that the cart exerts on the horse must be equal in magnitude to the force that the horse exerts on the cart (11ea6ebb_72d2_5ccd_9d78_691e8b8bf06e_TB6213_11). Thus, the answer is B, which is equal to the magnitude of 11ea6ebb_72d2_83de_9d78_f31df788d443_TB6213_11.

Question 4

You ride on an elevator that is moving downward with constant speed while standing on a bathroom scale. The reading on the scale is
A) equal to your true weight, mg.
B) more than your true weight, mg.
C) less than your true weight, mg.
D) could be more or less than your true weight, mg, depending on the value of the speed.

Accepted Answer

When the elevator moves downward with constant speed, there is no net acceleration acting on you. Therefore, the reading on the scale is equal to your true weight, mg.

Question 5

Imagine that the metal head of a hammer is loose. In order to get the hammerhead tight again you should
A) drop the hammer on its side from some given height.
B) drop the hammer with the handle end down.
C) drop the hammer with the head end down.
D) It makes no difference how you drop the hammer, the head will be tightened.
E) It makes no difference how you drop the hammer, the head will not be tightened.

Accepted Answer

Dropping the hammer with the handle end down causes the hammerhead to slide down the handle due to inertia, tightening it.

Question 6

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is
A) Mg.
B) Mg sin θ.
C) Mg cos θ.
D) Mg tan θ.
E) zero, since the plane is frictionless.

Accepted Answer

The normal force is perpendicular to the surface of the inclined plane and opposite to the weight of the object (which is Mg in this case, pointing straight down). Therefore, the vertical component of the weight is balanced by the normal force so that the block does not fall into the plane. Using trigonometry, the vertical component of the weight is Mg cos θ. So, the normal force (which is equal in magnitude and opposite in direction to the vertical component of the weight) is Mg cos θ.

Question 7

A person is lowering a bucket into a well with a constant speed. The force exerted by the rope on the bucket is
A) equal to the bucket's weight.
B) greater than the bucket's weight.
C) less than the bucket's weight, but not zero N.
D) zero N.
E) Cannot be determined without additional information.

Accepted Answer

Since the bucket is being lowered with a constant speed, the net force acting on the bucket must be zero. This means that the force of gravity pulling down on the bucket must be balanced by a force of equal magnitude pulling up on the bucket from the rope. This force is provided by tension in the rope, and its magnitude is equal to the weight of the bucket. Therefore, the force exerted by the rope on the bucket is equal to the bucket's weight.

Question 8

What does the word "normal" mean in the phrase "normal force"?
A) the force that is usually exerted by a surface
B) the total force exerted by a surface
C) the component of the force exerted by a surface parallel to the surface
D) the component of the force exerted by a surface perpendicular to the surface
E) the force is due to contact between two objects.

Accepted Answer

In physics, the normal force is the component of the force exerted by a surface perpendicular to the surface. It is called "normal" because it is at a right angle (or "normal" angle) to the surface.

Question 9

A golf club hits a golf ball with a force of 2400 N. The golf ball hits the club with a force
A) slightly less than 2400 N.
B) exactly 2400 N.
C) slightly more than 2400 N.
D) close to 0 N.
E) Cannot be determined without additional information.

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force exerted by the golf ball on the club is exactly 2400 N.

Question 10

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is directed
A) parallel to the plane in the same direction as the movement of the block.
B) parallel to the plane in the opposite direction as the movement of the block
C) perpendicular to the plane.
D) toward the center of the Earth.
E) toward the center of mass of the block.

Accepted Answer

The normal reaction force is always perpendicular to the surface of contact between two objects. In this case, it is perpendicular to the inclined plane.

Question 11

An object of weight W is in free-fall close to the surface of Earth. What is the force that the object exerts on Earth?
A) a force greater than W
B) a force less than W
C) a force equal to W
D) no force at all
E) cannot be determined without additional information

Accepted Answer

According to Newton's third law of motion, every action has an equal and opposite reaction. So, when the object is falling towards the surface of the Earth, it exerts a force (equal in magnitude and opposite in direction) on the Earth. This force is also known as the weight of the object, which is equal to W. Hence, the correct answer is C) a force equal to W.

Question 12

You ride on an elevator that is moving with constant downward acceleration while standing on a bathroom scale. The reading on the scale is
A) equal to your true weight, mg.
B) less than your true weight, mg.
C) more than your true weight, mg.
D) could be more or less than your true weight, mg, depending on the magnitude of the acceleration.

Accepted Answer

When the elevator accelerates downward, the normal force (which is what the scale reads) is reduced by the acceleration, making the scale reading less than your true weight.

Question 13

A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. Since a lot of damage is done on the car
A) the force on the truck is greater then the force on the car.
B) the force on the truck is equal to the force on the car.
C) the force on the truck is smaller than the force on the car.
D) the truck did not slow down during the collision.
E) the car did not slow down during the collision.

Accepted Answer

According to Newton's third law of motion, the force exerted by the truck on the car is equal in magnitude and opposite in direction to the force exerted by the car on the truck.

Question 14

A ball is thrown up into the air. Ignore air resistance. When it is rising and reaches half of its maximum height, the net force acting on it is
A) equal to its weight.
B) greater than its weight.
C) less than its weight, but not zero N.
D) zero N.
E) Cannot be determined without additional information.

Accepted Answer

The only force acting on the ball is gravity, which is equal to its weight, as air resistance is ignored.

Question 15

A truck is towing a car whose mass is one quarter that of the truck. The force exerted by the truck on the car is 6000 N. The force exerted by the car on the truck is
A) 1500 N.
B) 24000 N.
C) 3000 N.
D) 6000 N.
E) 12000 N.

Accepted Answer

According to Newton's third law of motion, the force exerted by the car on the truck is equal in magnitude and opposite in direction to the force exerted by the truck on the car, which is 6000 N.

Question 16

A student uses a plumb bob to verify that the doorjamb in a car is vertical. As the car pulls away from a stop, the student observes that the string now makes an angle θ with the doorjamb. What is the acceleration of the car?
A) g sin θ
B) g cos θ
C) g tan θ
D) g θ
E) θ

Accepted Answer

The angle θ indicates that the plumb bob is deflected due to the horizontal acceleration of the car. The horizontal component of the tension in the string is equal to the mass times the acceleration (ma), and the vertical component is equal to the weight (mg). Therefore, tan θ = a/g, which implies a = g tan θ.

Question 17

An object of mass m sits on a flat table. The Earth pulls on this object with force mg, which we will call the action force. What is the reaction force?
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, every action has an equal and opposite reaction. If the Earth pulls the object downward with force mg, the object pulls the Earth upward with the same force mg.

Question 18

You apply the same force to two objects. Object 1 has mass M and object 2 has mass 5M. The acceleration of object 2 is
A) ten times that of object 1.
B) five times that of object 1.
C) the same as that of object 1.
D) one-fifth as that of object 1.
E) has no relation to that of object 1.

Accepted Answer

According to Newton's second law, acceleration is inversely proportional to mass when the same force is applied. Therefore, object 2, having five times the mass of object 1, will have one-fifth the acceleration of object 1.

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 this force equals the weight of the fireman, what happens?
A) The fireman comes to a stop.
B) The fireman descends with slower and slower speed.
C) The fireman descends with a smaller acceleration.
D) The fireman continues to descend, but with constant speed.
E) Cannot be determined without additional information.

Accepted Answer

When the frictional force exerted by the pole equals the weight of the fireman, the net vertical force on the fireman becomes zero. Therefore, there is no further acceleration in the vertical direction. Since the fireman was already moving downwards, he will continue to move downwards with a constant speed. Hence, the correct option is (D).

Question 20

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The gravitational force is directed
A) parallel to the plane in the same direction as the movement of the block.
B) parallel to the plane in the opposite direction as the movement of the block
C) perpendicular to the plane.
D) toward the center of the Earth.
E) toward the center of mass of the block.

Accepted Answer

The gravitational force always acts toward the center of the Earth, regardless of the block's movement or orientation of the plane.

Quiz 5: Newtons Laws of Motion

FIGURE 5-1 -In Figure 5-1, masses m1 and m2 are such that m1 > m2 and they lay on a level, frictionless surface. We can apply a horizontal force either from the left or from the right. The contact force between masses m1 and m2 is

A locomotive is pulling a number of identical wagons along a level track and accelerating. Friction is negligible. Starting from the last wagon, the ratio of the forces between adjacent wagons is

A horse pulls a cart with force . As a result of this force the cart accelerates with constant acceleration. What is the magnitude of the force that the cart exerts on the horse?

You ride on an elevator that is moving downward with constant speed while standing on a bathroom scale. The reading on the scale is

Imagine that the metal head of a hammer is loose. In order to get the hammerhead tight again you should

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is

A person is lowering a bucket into a well with a constant speed. The force exerted by the rope on the bucket is

What does the word "normal" mean in the phrase "normal force"?

A golf club hits a golf ball with a force of 2400 N. The golf ball hits the club with a force

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is directed

An object of weight W is in free-fall close to the surface of Earth. What is the force that the object exerts on Earth?

You ride on an elevator that is moving with constant downward acceleration while standing on a bathroom scale. The reading on the scale is

A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. Since a lot of damage is done on the car

A ball is thrown up into the air. Ignore air resistance. When it is rising and reaches half of its maximum height, the net force acting on it is

A truck is towing a car whose mass is one quarter that of the truck. The force exerted by the truck on the car is 6000 N. The force exerted by the car on the truck is

A student uses a plumb bob to verify that the doorjamb in a car is vertical. As the car pulls away from a stop, the student observes that the string now makes an angle θ with the doorjamb. What is the acceleration of the car?

An object of mass m sits on a flat table. The Earth pulls on this object with force mg, which we will call the action force. What is the reaction force?

You apply the same force to two objects. Object 1 has mass M and object 2 has mass 5M. The acceleration of object 2 is

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 this force equals the weight of the fireman, what happens?

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The gravitational force is directed

FIGURE 5-1 -In Figure 5-1, masses m₁ and m₂ are such that m₁ > m₂ and they lay on a level, frictionless surface. We can apply a horizontal force either from the left or from the right. The contact force between masses m₁ and m₂ is