AP Physics C: Mechanics : Mechanics Exam

Study concepts, example questions & explanations for AP Physics C: Mechanics

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Example Questions

Example Question #91 : Ap Physics C

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Example Question #92 : Ap Physics C

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Example Question #93 : Ap Physics C

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Example Question #15 : Friction And Normal Force

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Normal

Example Question #94 : Ap Physics C

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Normal

Example Question #1 : Understanding Gravity

A block with a mass of  is traveling at  when it impacts the ground. From how many meters off the ground was the block dropped?

Round to the nearest whole number.

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Correct answer:

Explanation:

Set the gravitational potential energy and kinetic energy equal to each other and solve for the height.

Mass cancels.

Isolate the height and plug in our values.

Rounding this gives .

Example Question #92 : Ap Physics C

An object of mass  is dropped from a tower. The object's drag force is given by  where  is a positive constant. What will the objects terminal velocity be?

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Explanation:

To find terminal velocity, set the magnitude of the drag force equal to the magnitude of the force of gravity since when these forces are equal and opposite, the object will stop accelerating:

Solve for 

Example Question #1 : Gravity

A ship of mass  and an initial velocity of  is coasting to a stop. The water exerts a drag force on the ship. The drag force is proportional to the velocity:

 where the negative sign indicates that the drag force acts in a direction opposite the motion. After the ship has coasted for a time equal to , how fast (in terms of ) will the ship be moving?

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Correct answer:

Explanation:

The ship's equation of velocity (found by solving the first-order differential equation) is 

Substitute  and solve.

Example Question #93 : Ap Physics C

A spherical asteroid has a hole drilled through the center as diagrammed below:

Hole through planet

Refer to the diagram above. An object that is much smaller than the asteroid is released from rest at the surface of the asteroid, at point a. How do the velocity and acceleration of the object compare at point b at the surface, and point a, located at the center of the asteroid?

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Correct answer:

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Explanation:

Because the gravitational force depends only on the mass beneath the object (which is the gravitational version of Gauss's Law for charge), the acceleration steadily decreases as the object falls, and drops to zero at the center. Nevertheless, the velocity keeps increasing as the object falls, it just does so more slowly.

Example Question #91 : Mechanics Exam

With what minimum velocity must a rocket be launched from the surface of the moon in order to not fall back down due to the moon's gravity?

The mass of the moon is  and its radius is .

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Correct answer:

Explanation:

Relevant equations:

For the rocket to escape the moon's gravity, its minimum total energy is zero. If the total energy is zero, the rocket will have zero final velocity when it is infinitely far from the moon. If total energy is less than zero, the rocket will fall back to the moon's surface. If total energy is greater than zero, the rocket will have some final velocity when it is infinitely far away. 

For the minimum energy case as the rocket leaves the surface:

Rearrange energy equation to isolate the velocity term.

Substitute in the given values to solve for the velocity.

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