Question 1

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

Accepted Answer

When an object is thrown upward, the force of wind resistance is acting in the direction opposite to the object's velocity. At the moment it is released, the object has an initial velocity of zero, and so the force of wind resistance is also zero. As the object moves upward, its speed increases, and therefore the force of wind resistance also increases. Thus, the acceleration of the object is highest immediately after it's released.

Question 2

Two bodies P and Q on a perfectly smooth horizontal surface are connected by a light cord.The mass of P is greater than that of Q.A horizontal force  is applied to Q as shown in the figure,accelerating the bodies to the right.  The magnitude of the force exerted by the connecting cord on body P will be
A)zero.
B)less than F but not zero.
C)equal to F.
D)greater than F.

Accepted Answer

The answer of Two bodies P and Q on a...

Question 3

A large truck collides head-on with a cyclist.During the collision
A)the truck exerts the same amount of force on the cyclist as the cyclist exerts on the truck.
B)the truck exerts a greater amount of force on the cyclist than the cyclist exerts on the truck.
C)the truck exerts a smaller amount of force on the cyclist than the cyclist exerts on the truck.
D)the truck exerts a force on the cyclist,but the cyclist exerts no force on the truck.

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the truck exerts the same amount of force on the cyclist as the cyclist exerts on the truck.

Question 4

If you jumped out of a plane,you would begin speeding up as you fall downward.Eventually,due to wind resistance,your velocity would become constant with time.After this occurs,the magnitude of the force of wind resistance is
A)equal to the force of gravity acting on you.
B)is much smaller than the force of gravity acting on you.
C)is slightly smaller than the force of gravity acting on you.
D)is greater than the force of gravity acting on you.

Accepted Answer

When your velocity becomes constant, you have reached terminal velocity, where the force of wind resistance equals the force of gravity, resulting in no net acceleration.

Question 5

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

Accepted Answer

Friction is the force that opposes motion between two surfaces in contact. If there is no friction between the ice and the puck, there is no opposing force to slow the puck down after it leaves your stick. Therefore, the puck will continue to move at a constant speed in the same direction.

Question 6

When decelerating quickly in a car,you feel as if you are being thrown forward in your seat.Which one of Newton's Laws most directly explains this effect? Explain your reasoning.

Accepted Answer

The answer of When decelerating quickly in a car,you feel...

Question 7

A dog is standing in the tail bed of a pickup truck.The tail 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 simply slides toward the back of the truck.
B)moves to the right,but not as quickly as the truck is moving to the right,causing it to slide toward 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 toward the back of the truck.

Accepted Answer

Since there is no force of friction between the dog and the truck due to the icy surface, the dog will not move to the right along with the truck. Instead, it will simply slide toward the back of the truck as the truck accelerates. Therefore, option A is the correct choice.

Question 8

An object is moving with a constant velocity.Which statement(s)MUST be true?
A)The net force on the object is zero.
B)A small net force is acting on the object,in the direction of motion.
C)No forces are acting on the object.
D)Two of the above statements are true.

Accepted Answer

When an object is moving with a constant velocity, it means that there is no acceleration. According to the second law of motion, acceleration is directly proportional to the net force acting on the object. Therefore, if there is no acceleration, it means that there is no net force acting on the object. Hence, statement A, "The net force on the object is zero", must be true. Statements B and C are not necessarily true in this case.

Question 9

A person gives a shopping cart an initial push along a horizontal floor to get it moving,and then lets go.The cart travels forward along the floor,gradually slowing as it moves.Consider the horizontal force(s)on the cart while it is moving forward and slowing.Which of the following statements is correct?
A)Both a forward and a backward force are acting on the cart,but the forward force is larger.
B)Both a forward and a backward force are acting on the cart,but the backward force is larger.
C)Only a forward force is acting,which diminishes with time.
D)Only a backward force is acting,no forward force.

Accepted Answer

According to Newton's Third Law, for every action, there is an equal and opposite reaction. The force applied by the person initially pushing the cart forward creates an equal and opposite force in the backward direction on the cart. This force acting in the opposite direction is known as friction. As the cart moves forward and slows down, the force of friction continues to act in the opposite direction, gradually reducing the cart's speed. Therefore, only a backward force is acting on the cart, and there is no forward force acting once the initial push has stopped.

Question 10

You are making a circular turn in your car when you hit a big patch of ice,causing the force of friction between the tires and the road to become zero.While the car is on the ice,it
A)moves along a straight-line path.
B)continues to follow a circular path,but with a radius larger than the original radius.
C)moves along a path that is neither straight nor circular.
D)continues to follow the same circular path as initially.

Accepted Answer

When the force of friction between the tires and the road becomes zero, there is nothing to provide the necessary centripetal force for the car to continue following a circular path. Therefore, the car will move along a straight-line path in the direction of the velocity it had at the moment when the tires lost grip on the road.

Question 11

In outer space,an astronaut is working with two pieces of equipment that are outwardly identical.However,one of the objects has a slightly larger mass than the other.Since objects are weightless in space,how can the astronaut distinguish between the two objects?

Accepted Answer

The answer of In outer space,an astronaut is working with...

Question 12

Your younger brother is supposed to mow the lawn using a push mower.He reasons from Newton's Third Law that the mower will push back with the same force he exerts on the mower;therefore nothing will move and attempting to mow the lawn is pointless.What is wrong with his reasoning?

Accepted Answer

The answer of Your younger brother is supposed to mow...

Question 13

Explain,in terms of Newton's Laws,why a quick jerk on a string may cause it to break,while the same change in momentum performed over a longer time will not.

Accepted Answer

The answer of Explain,in terms of Newton's Laws,why a quick...

Question 14

Newton's Third Law suggests that a book sitting on a flat table experiences an upward force due to the table.If this is true,why doesn't the book start moving upward?

Accepted Answer

The answer of Newton's Third Law suggests that a book...

Question 15

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)None of the above

Accepted Answer

At the highest point, the velocity of the ball is zero, but the acceleration due to gravity is still acting downward, and the force of gravity is also directed downward.

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 directed to the right, it means there is an unbalanced force acting on the object in the same direction as its motion. The magnitude of the force decreasing means that the acceleration of the object is decreasing with time. However, since there is still a net force acting on the object, it will continue to accelerate in the right direction, meaning its speed is increasing.

Question 17

A woman is straining to lift a large crate,without success.It is too heavy.We denote the forces on the crate as follows: P is the upward force being exerted on the crate by the person,C is the 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 A woman is straining to lift a...

Question 18

A ball is thrown vertically upward,reaches a highest point,and comes back down.At the top of its path,what forces,if any,act on the ball? Explain your answer.
A)no forces
B)only a downward force
C)only an upward force
D)an upward and a downward force,opposing and equal

Accepted Answer

At the top of its path, the only force acting on the ball is gravity, which is a downward force.

Question 19

Bill and Susan are both standing on identical skateboards (with really good ball bearings),initially at rest.Bill weighs three times as much as Susan.Bill pushes horizontally on Susan's back,causing Susan to start moving away from Bill.Immediately after Bill stops pushing,
A)Susan and Bill are moving away from each other,and Susan's speed is three times that of Bill.
B)Susan is moving away from Bill,and Bill is stationary.
C)Susan and Bill are moving away from each other,with equal speeds.
D)Susan and Bill are moving away from each other,and Susan's speed is three times less than that of Bill.

Accepted Answer

According to the law of conservation of momentum, the momentum of the system must remain zero since they started from rest. If Bill weighs three times as much as Susan, then Susan's speed will be three times that of Bill's in the opposite direction to conserve momentum.

Question 20

A stalled car is being pushed up a hill by three people,and it is moving at a constant speed.The net force on the car is
A)zero.
B)in the same direction of the car's motion.
C)in the opposite direction of the car's motion.
D)None of the above

Accepted Answer

If the car is moving at a constant speed, then the net force on the car must be zero. This means that the force being exerted by the three people pushing the car up the hill must be equal and opposite to the force of friction acting against the car. Therefore, the net force is balanced and equal to zero.

Quiz 4: Forces and Newtons Laws of Motion

Suppose the force of wind resistance is proportional to the speed of the object and in the direction opposite the object's velocity.If you throw an object upward,when is the magnitude of the acceleration the highest?

A large truck collides head-on with a cyclist.During the collision

If you jumped out of a plane,you would begin speeding up as you fall downward.Eventually,due to wind resistance,your velocity would become constant with time.After this occurs,the magnitude of the force of wind resistance is

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

When decelerating quickly in a car,you feel as if you are being thrown forward in your seat.Which one of Newton's Laws most directly explains this effect? Explain your reasoning.

An object is moving with a constant velocity.Which statement(s) MUST be true?

You are making a circular turn in your car when you hit a big patch of ice,causing the force of friction between the tires and the road to become zero.While the car is on the ice,it

In outer space,an astronaut is working with two pieces of equipment that are outwardly identical.However,one of the objects has a slightly larger mass than the other.Since objects are weightless in space,how can the astronaut distinguish between the two objects?

Your younger brother is supposed to mow the lawn using a push mower.He reasons from Newton's Third Law that the mower will push back with the same force he exerts on the mower;therefore nothing will move and attempting to mow the lawn is pointless.What is wrong with his reasoning?

Explain,in terms of Newton's Laws,why a quick jerk on a string may cause it to break,while the same change in momentum performed over a longer time will not.

Newton's Third Law suggests that a book sitting on a flat table experiences an upward force due to the table.If this is true,why doesn't the book start moving upward?

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

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 ball is thrown vertically upward,reaches a highest point,and comes back down.At the top of its path,what forces,if any,act on the ball? Explain your answer.

Bill and Susan are both standing on identical skateboards (with really good ball bearings) ,initially at rest.Bill weighs three times as much as Susan.Bill pushes horizontally on Susan's back,causing Susan to start moving away from Bill.Immediately after Bill stops pushing,

A stalled car is being pushed up a hill by three people,and it is moving at a constant speed.The net force on the car is