AP Physics 1 : Circular and Rotational Motion

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #71 : Circular And Rotational Motion

A child is swinging a toy rocket around their head with a rope. If they double the frequency of "orbits", how will the tension in the rope change?

Possible Answers:

Quadrupled

Halved

Quartered

None of these

Doubled

Correct answer:

Quadrupled

Explanation:

The tension in the rope is equal to the centripetal force on the rocket.

Definition of velocity:

The time necessary to go around one circle is it's period, which is the inverse of the frequency.

Doubling the frequency would double the velocity, which would quadruple the tension.

Example Question #72 : Circular And Rotational Motion

A bus is traveling with a constant linear velocity around a corner. Which of the following is true?

Possible Answers:

There is no net force on the bus.

The bus is accelerating since it is changing directions.

The bus is accelerating since it has constant velocity.

The bus is not accelerating since it has constant velocity.

The bus is not accelerating since it has constant speed.

Correct answer:

The bus is accelerating since it is changing directions.

Explanation:

The bus going around a corner is experiencing centripetal acceleration towards the center of it's turn. Even though the linear velocity is constant (speed), the bus is constantly changing directions, thus its velocity is not constant. Since acceleration is defined as the change in velocity over time, the acceleration is nonzero, which means that due to Newton's second law, the net force on the bus is also nonzero.

Example Question #31 : Centripetal Force And Acceleration

A bowling ball with radius  is traveling at a linear velocity of . What is the centripetal acceleration at a point within the bowling ball that is  from the center?

Possible Answers:

Correct answer:

Explanation:

To calculate the centripetal acceleration at the point identified in the expression (which is simply ), we need to determine the linear velocity at this point. We can do this by using the period of the bowling ball:

Where both the circumference and velocity are referenced to the outer surface of the bowling ball:

Plugging in our values, we get:

This is the time it takes for any single point of the ball (inside or out, excluding the center) to complete one full rotation. Therefore, we can apply this same expression to the point asked in the question (r=0.05m):

Rearranging for velocity, we get:

Plugging in our values, we get:

Example Question #31 : Centripetal Force And Acceleration

If the centripetal acceleration of the outside of a bowling ball with mass  and radius  is , what is the total kinetic energy of the ball?

Possible Answers:

Correct answer:

Explanation:

The total kinetic energy of a solid sphere can be calculated using the following:

Where I is the moment of inertia for a solid sphere:

And w is the angular velocity:

Plugging these in, we get:

We can obtain an expression for velocity using the expression for centripetal acceleration:

Rearranging:

Plugging this in, we get:

We have all of these values, so let's plug them in:

Example Question #71 : Circular And Rotational Motion

A block of mass is attached to the end of a string. Determine the minimum angular velocity needed to keep the string taught while the block is swung in vertical circles.

Possible Answers:

None of these

Correct answer:

Explanation:

At the top of the swing, both gravity and the tension of the string will be in the same direction, thus, this is where tension would be at a minimum. 

At the very limit of being taught, 

Thus,

Solving for 

This will be the linear velocity.

The angular velocity will be 

Combining equations

Plugging in values

Example Question #121 : Circular, Rotational, And Harmonic Motion

A block of mass  is attached to the end of a  string. Determine the minimum angular velocity needed to keep the string taught while the block is swung in vertical circles.

Possible Answers:

None of these

Correct answer:

Explanation:

At the top of the swing, both gravity and the tension of the string will be in the same direction, thus, this is where tension would be at a minimum. 

At the very limit of being taught, 

Thus,

Solving for 

This will be the linear velocity.

The angular velocity will be 

Combining equations

Plugging in values

Example Question #41 : Centripetal Force And Acceleration

Troy spins a ball attached to a string around in a vertical circle. Assume the ball travels at constant speed during its circular path. Which of the following is not constant throughout the ball's path?

Possible Answers:

Tension in the string

Force of gravity on the ball

The rate at which the string does work on the ball

All of these are constant

Angular momentum of the ball

Correct answer:

Tension in the string

Explanation:

Let's go through each answer choice one by one. The force of gravity on the ball is always its mass times gravity, which is constant. The string's pull on the ball is always perpendicular to the ball's motion, so it isn't doing any work, and thus has a constant rate of work . The ball's angular momentum is always constant since its mass, the radius of the circle it's traveling in, and its speed are constant. The only the changing is the tension in the string. This is true because the ball needs the same center pulling force (centripetal force) throughout its path, but this centripetal force is constantly changing direction. For example, at the top of its path, the centripetal force must be down because that's the direction of the center of its circle of motion, but at the bottom, the centripetal force must be up. There are two forces on the ball, gravity and tension. The force of gravity is always down and constant, so the tension needs to change in order to keep the center pulling force the same. For example, when the ball is at the bottom of the circle, the force of gravity is away from the center of the circle, so tension must be higher to keep the center pull constant.

Example Question #42 : Centripetal Force And Acceleration

An airplane is traveling at  and performs a vertical loop in . Determine the net force on the  pilot at the bottom of the loop.

Possible Answers:

None of these

Correct answer:

Explanation:

Circumference of a circle:

Distance plane travels during loop (which will be the circumference)

Centripetal acceleration:

Plugging in values:

Example Question #41 : Centripetal Force And Acceleration

An airplane is traveling at  and performs a vertical loop in . Determine the force due to the seat on the  pilot at the bottom of the loop

Possible Answers:

None of these

Correct answer:

Explanation:

Circumference of a circle:

Distance plane travels during loop (which will be the circumference)

Centripetal acceleration:

Plugging in values:

Example Question #41 : Centripetal Force And Acceleration

An airplane is traveling at  and performs a vertical loop in . Determine the radius of the loop.

Possible Answers:

Correct answer:

Explanation:

Circumference of a circle:

Distance plane travels during loop (which will be the circumference)

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