AP Physics 1 : Linear Motion and Momentum

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #61 : Impulse And Momentum

 man is running at . From that run, he jumps on a skateboard of mass of . Assuming no energy lost to friction, determine the impulse experienced by the board

Possible Answers:

None of these

Correct answer:

Explanation:

Using conservation of momentum:

The man and the skateboard are stuck together, and thus become one mass:

Plugging in values:

Solving for 

 

Definition of impulse:

Since initial momentum was zero:

Example Question #61 : Impulse And Momentum

Two identical rockets are placed on the back of cars. Car  has a mass twice that of car . The rockets are identically fired for , then shut off.

How do the final velocities of the cars compare?

Possible Answers:

The velocity of the lighter car will be one-fourth that of the heavier car

They will be the same

The velocity of the lighter car will be half that of the heavier car

None of these

The velocity of the heavier car will be half that of the lighter car

Correct answer:

The velocity of the heavier car will be half that of the lighter car

Explanation:

Using 

It can be seen that since both cars have the same force applied for equal amount of time, they have identical final momentums.

Using

Where  is momentum,  is mass, and  is velocity

It can be seen that if momentum is held constant, and mass is doubled, velocity will be cut in half.

Example Question #61 : Impulse And Momentum

Two identical rockets are placed on the back of cars. Car  has a mass twice that of car . The rockets are identically fired for , then shut off.

How do the final kinetic energies of the cars compare?

Possible Answers:

The lighter car will have four times the kinetic energy

None of these

The heavier car will have half the kinetic energy

The heavier car will have one-fourth the kinetic energy

The heavier car will have twice the kinetic energy

Correct answer:

The heavier car will have half the kinetic energy

Explanation:

Using 

It can be seen that since both cars have the same force applied for equal amount of time, they have identical final momentums.

Using

It can be seen that if momentum is held constant, and mass is doubled, then the kinetic energy of the heavier car will be half.

Example Question #61 : Impulse And Momentum

 man is running at . From that run, he jumps on a skateboard of mass of . Assuming no energy lost to friction, determine the impulse experienced by the board

Possible Answers:

None of these

Correct answer:

Explanation:

Using conservation of momentum:

The man and the skateboard are stuck together, and thus become one mass:

Plugging in values:

Solving for 

 

Definition of impulse:

Since initial momentum was zero:

Example Question #64 : Impulse And Momentum

 man is running at . From that run, he jumps on a resting skateboard of mass of . Assuming no energy lost to friction, determine the final velocity of the man on the board.

Possible Answers:

None of these

Correct answer:

Explanation:

Using conservation of momentum:

The man and the skateboard are stuck together, and thus become one mass:

Plugging in values:

Solving for 

Example Question #71 : Impulse And Momentum

A blob in space of mass  is moving in a straight line at . It then collides and sticks to another blob that was previously stationary. The final velocity of the combined blobs is . Find the mass of the second blob.

Possible Answers:

None of these

Correct answer:

Explanation:

Using

Plugging in values:

Example Question #72 : Impulse And Momentum

A  ping pong ball is accelerating at . Determine the net force on the ball.

Possible Answers:

Correct answer:

Explanation:

Using

Converting  to  and plugging in values

Example Question #73 : Impulse And Momentum

A bullet weighing  is fired at a velocity of  at a block weighing  at rest on a frictionless surface. When the bullet hits the block, it becomes lodged in the block and causes the block to move. How fast does the block move after the collision?

Possible Answers:

Correct answer:

Explanation:

Using the equation of momentum,

we can compare the initial and final scenarios and set them equal to each other to solve for the final velocity of the block (don't forget to convert the units of  to !):

Example Question #74 : Impulse And Momentum

tennis ball hits a wall head-on with a forward speed of . It rebounds with a speed of . The contact time is . What is the impulse with the wall?

Possible Answers:

Correct answer:

Explanation:

Impulse is defined as a change in momentum:

Pay attention to direction, because this changes the sign!

Example Question #75 : Impulse And Momentum

Force 1 acts on an object for  with . Force 2 acts on an object for  with .

Which force changes the momentum of the object more?

Possible Answers:

Force 1

It's impossible to tell.

There is no momentum change in either situation.

Force 1 and Force 2 change the momentum of the object the same amount.

Force 2

Correct answer:

Force 1 and Force 2 change the momentum of the object the same amount.

Explanation:

The impulse momentum theorem states:

Where  is the change in momentum of an object,  is the force acting on the object, and  is the amount of time the force acts on the object.

The change in momentum due to Force 1 can be found by:

And the change in momentum due to Force 2 can be found by:

So both situations produce the same change in momentum.

It's important to understand that both force and time have a linear relationship with momentum, meaning that as either force and/or time increase, momentum will also increase.

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