AP Physics 1 : Circular and Rotational Motion

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #7 : Period And Frequency

Two cars are racing side by side on a perfectly circular race track. The inner car is from the center of the track. The outer car is from center of the track. Both cars are traveling at .

How long does it take the inner car to complete a lap?

Possible Answers:

Correct answer:

Explanation:

Finding distance of lap of inner car:

Convert  to :

Use the distance formula:

Example Question #8 : Period And Frequency

Two cars are racing side by side on a perfectly circular race track. The inner car is from the center of the track. The outer car is from center of the track. Both cars are traveling at 

How much longer does it take the outer car to complete one lap?

Possible Answers:

Correct answer:

Explanation:

Inner car time:

Finding distance of lap of inner car:

Convert  to :

Use the distance formula:

Finding distance of lap of outer car:

Convert  to :

Use the distance formula:

Example Question #9 : Period And Frequency

A car with wheels of mass and wheels of radius is traveling at . Treating the wheels as disks of uniform mass density, calculate the angular frequency of one wheel.

Possible Answers:

None of these

Correct answer:

Explanation:

Example Question #10 : Period And Frequency

A car with wheels of mass and wheels of radius is traveling at . Treating the wheels as disks of uniform mass density, calculate the angular period of one wheel.

Possible Answers:

None of these

Correct answer:

Explanation:

First, find the angular frequency:

Angular period is the inverse of angular frequency:

Example Question #121 : Circular And Rotational Motion

A bowling ball of mass  and radius  is thrown with a rotational kinetic energy of . Find its period.

Possible Answers:

Correct answer:

Explanation:

The expression for rotational kinetic energy is:

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

And w is the angular velocity:

Plugging these in, we get:

Rearranging for linear velocity:

The expression for period is the circumference of the ball divided by the linear velocity of the ball:

Plugging in expressions, we get:

We have all of these values, so time to plug and chug:

Example Question #122 : Circular And Rotational Motion

A ferris wheel has a diameter of 60 meters. The carriages on the outside of the wheel are traveling at an instantaneous velocity of . What is the period of rotation of the wheel?

Possible Answers:

Correct answer:

Explanation:

We can calculate the circumference of the wheel using the given radius:

We can use this and the given velocity to find the period:

Example Question #21 : Motion

A wheel of radius  rolls along a flat floor and makes  rotations over a period of time. What distance  has the wheel traveled?

Possible Answers:

Correct answer:

Explanation:

In order to find the distance the wheel travels, we need a way to convert angular displacement to linear displacement. We know that the circumference of a circle (or a wheel, in this case) is . This means that in one rotation, the wheel would travel a distance equal to its circumference.

Distance of one rotation equals: .

Since the wheel travels  rotations, the total distance that the wheel travels will be equal to the distance traveled by one rotation multiplied by the number of rotations.

Distance of rotations equals:

Example Question #1 : Other Circular And Rotational Motion Concepts

A track runner who weighs 750 N is running around a curve at a speed of  in an arc whose radius, , is 6.0 m. Find the centripetal force acting on him.

Possible Answers:

Correct answer:

Explanation:

The equation for centripetal force on an object moving at a constant speed in a circular path is

The weight of the person is given to be .  Assuming , we can find the mass of the person using the equation

We are given the velocity, , and the radius, .  So, we can now solve for the centripetal force:

Example Question #2 : Other Circular And Rotational Motion Concepts

A 55 cm rope is tied to the handle of a bucket, which is then spun in a vertical circle. The mass of the bucket is 3.3 kg. What is the minimum speed required such that the rope does not become slack when the bucket reaches the highest point in the circle?

Possible Answers:

Correct answer:

Explanation:

The faster that the object is moving while being spun, the greater the force of tension in the rope will be. Therefore, if we want to find the minimum speed of the bucket at the highest point in the circle such that the rope doesn't go slack, we should assume that the tension at that point is zero.

If the tension is zero, then the only force acting on the bucket at that point would be the force of gravity pulling down on the bucket. If the rope does not go slack, then the bucket must still be moving in a circular motion, so we can use the equation for circular/centripetal motion:

Since gravity is the only force, then

We can divide by  on both sides to cancel that out, and then solve for :

The radius was given to us as 55 cm. We have to convert this to meters. Since , we should divide by 100 to get .  Now, plug that into the equation above and solve for velocity:

Example Question #1 : Other Circular And Rotational Motion Concepts

Bob is riding a merry-go-round. He is 10 meters from the center and the merry-go-round completes two revolutions per minute. What is the centripetal acceleration acting on Bob?

Possible Answers:

Correct answer:

Explanation:

The formula for centripetal acceleration is:

First, we need to solve for velocity by taking the distance Bob travels and dividing by the time it takes to travel that distance. The distance he travels is the circumference of the circle, and the time is 30 seconds, because the merry-go-round completes two revolutions per minute, or one revolution every thirty seconds:

Therefore,

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