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AP Physics Rotational Motion

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Section 1

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A radian is:

Front

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Last updated

1 year ago

Date created

Mar 14, 2020

Cards (17)

Section 1

(17 cards)

A radian is:

Front

Dimensionless Quantity, Ratio of Arc Length over Radius, Unit for Rotational Position

Back

Suppose that the speedometer of a truck is set to read the linear speed of the truck, but uses a device that actually measures the angular speed of the tires. If larger diameter tires are mounted on the truck instead, how will that affect the speedometer reading as compared to the true linear speed of the truck?

Front

speedometer reads a lower speed than the true linear speed - The linear speed is v = wR. So when the speedometer measures the same angular speed w as before, the linear speed v is actually higher, because the tire radius is larger than before.

Back

An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle q in the time t, through what angle did it rotate in the time 1/2 t?

Front

1/4 angle - The angular displacement is q = 1/2 at 2 (starting from rest), and there is a quadratic dependence on time. Therefore, in half the time, the object has rotated through one-quarter the angle.

Back

A person with moment of inertia I is spinning with an angular velocity ω. What will the angular velocity of the person be if he moves his arm position such that his moment of inertia changes to (3/4)I?

Front

(4/3) ω

Back

If the angular speed of a rotating rigid body is doubled, how will its rotational kinetic energy change, if at all?

Front

Be quadrupled

Back

Bonnie sits on the outer rim of a merry-go-round, and Klyde sits midway between the center and the rim. The merry-go-round makes one complete revolution every two seconds. Klyde's angular velocity is:

Front

same as Bonnie's. - The angular velocity w of any point on a solid object rotating about a fixed axis is the same. Both Bonnie and Klyde go around one revolution every two seconds.

Back

Two forces produce the same torque. Does it follow that they have the same magnitude?

Front

no - Because torque is the product of force times distance, two different forces that act at different distances could still give the same torque.

Back

Which of the following quantities will impact how a rigid body's rotational speed can change?

Front

- The body's rotational inertia - The net torque on the body

Back

TRUE or FALSE; all points along a rotating rigid body move with a constant speed.

Front

FALSE

Back

Bonnie sits on the outer rim of a merry-go-round, and Klyde sits midway between the center and the rim. The merry-go-round makes one revolution every two seconds. Who has the larger linear (tangential) velocity?

Front

Bonnie - Their linear speeds v will be different since v = Rw and Bonnie is located further out (larger radius R) than Klyde.

Back

You exert a force on a friend who is holding a 4.0-m-long rope. Now suppose you exert the same force on your friend, but the friend is holding an 8.0-m-long rope. How will this affect the rotational acceleration?

Front

It will be half

Back

A person with moment of inertia I is spinning with an angular velocity ω. By which factor will the kinetic energy K of the person change if he moves his arm position such that his moment of inertia changes to 2I?

Front

(1/4)

Back

Two spheres have the same radius and equal masses. One is made of solid aluminum, and the other is made from a hollow shell of gold. Which one has the bigger moment of inertia about an axis through its center?

Front

hollow gold - Moment of inertia depends on mass and distance from axis squared. It is bigger for the shell since its mass is located farther from the center.

Back

An object at rest begins to rotate with a constant angular acceleration. If this object has angular velocity w at time t, what was its angular velocity at the time 1/2 t?

Front

1/2 w - The angular velocity is w = at (starting from rest), and there is a linear dependence on time. Therefore, in half the time, the object has accelerated up to only half the speed.

Back

When a tape is played on a cassette deck, there is a tension in the tape that applies a torque to the supply reel. Assuming the tension remains constant during playback, how does this applied torque vary as the supply reel becomes empty?

Front

torque decreases - As the supply reel empties, the lever arm decreases because the radius of the reel (with tape on it) is decreasing. Thus, as the playback continues, the applied torque diminishes.

Back

You are using a wrench to tighten a rusty nut. Which arrangement will be the most effective in tightening the nut?

Front

Since the forces are all the same, the only difference is the lever arm. The arrangement with the largest lever arm (case #2) will provide the largest torque.

Back

Consider two balls rolling down an inclined plane. One ball has moment of inertia I; the other has moment of inertia 2I. Both balls start from rest at the same height and have the same mass m. Which ball will reach the bottom of the inclined plane first?

Front

The ball with the moment of inertia I

Back