AP Random Review

If the speed of an object moving in a straight line is increasing at a constant rate, the net force acting on the object is

• zero

• constant, but not zero

• decreasing at a constant rate

• increasing at a constant rate

• changing at a rate proportional to the average velocity

A hoop of mass m and radius r rolls with constant speed on a horizontal surface without slipping. What is the hoop’s translational kinetic energy divided by its rotational kinetic energy?

• 4

• 2

• 1

• ½

• ¼

The rotational inertia of a sphere of mass M and radius R about a diameter is (2/5)MR². The rotational inertia about an axis tangent to the sphere is

• (3/2)MR²

• (7/5)MR²

• MR²

• (1/2)MR²

• (2/5)MR²

All of the following are vector quantities EXCEPT

• rotational kinetic energy

• torque

• angular momentum

• angular velocity

• centripetal acceleration

A wheel with rotational inertia 0.04 kg•m² and radius 0.02 m is turning at the rate of 10 revolutions per second when a frictional torque is applied to stop it. How much work is done by the torque in stopping the wheel?

• -0.0008 J

• -0.4π J

• -2 J

• -2π² J

• -8π² J

Object X of mass m is moving to the right with a speed of 3 m/s when it collides with object Y of mass m that is moving to the right with a speed of 2 m/s, as shown. After the collision, X is moving to the right with a speed of 2 m/s and Y is moving to the right with a speed of 3 m/s. Which of the following is true of the collision?

• It is elastic because momentum is conserved.

• It is elastic because kinetic energy is conserved.

• It is inelastic because momentum is not conserved.

• It is inelastic because kinetic energy is not conserved.

• More information is needed to determine whether the collision is elastic or inelastic.

A 20 kg box moving at an initial speed of 10 m/s slides 25 m to the right on a horizontal floor before it comes to a complete stop. What is the coefficient of friction between the box and the floor?

• 0.10

• 0.20

• 0.40

• 0.60

• 0.80

A 20 kg box moving at an initial speed of 10 m/s slides 25 m to the right on a horizontal floor before it comes to a complete stop. Which of the following best describes the

frictional forces exerted on the box and on the floor while the box is sliding?

• Box: none; Floor: none

• Box: to the right; Floor: to the right

• Box: to the right; Floor: to the left

• Box: to the left; Floor: to the none

• Box: to the left; Floor: to the right

The uniform rod of length L shown is supported by holding end X so that the rod makes an angle 60° with the horizontal floor. There is no friction acting between the rod and the floor. When the support at X is removed, the rod falls under the influence of gravity. Which of the following best describes the movement of end Y as the rod falls?

• It moves ½ L to the left.

• It remains at rest.

• It moves ¼ L to the right.

• It moves ½ L to the right.

• It moves ¾ L to the right.

In an experiment, an object is released from rest from the top of a building. Its speed v is measured as it reaches a point that is a distance d from the point of release. If this distance was doubled, what would the new speed be, assuming air resistance is negligible?

• v

•  $\sqrt{2}$ v

• 2 v

• 4 v

• 8 v