Torque Test Review

Pulleys X and Y are each attached to a block by a string that wraps around the pulley. Both blocks are released and have the same linear acceleration a. As the blocks fall, the pulleys rotate about their centers. Pulley Y has a larger radius than Pulley X. How does the angular acceleration αX of Pulley X compare to the angular acceleration αY of Pulley Y?

• αX > αY

• αX < αY

• αX = αY

• The angular accelerations cannot be determined without knowing the mass of each block.

Tags

NGSS.HS-PS2-1

The disk shown in the top-view figures is on a horizontal surface and is free to move with negligible friction. In both figures, two forces of magnitude F are exerted on the disk at the locations and in the directions shown. Which of the following correctly indicates whether the net torque exerted on the disk about its center of mass is greater in Figure 1 or Figure 2, and provides a valid justification?

• Figure 1, because both forces exert a clockwise torque.

• Figure 1, because the net force on the disk is greater.

• Figure 2, because the line of action of one of the forces passes through the center of mass.

• Figure 2, because the forces in Figure 1 cancel each other out.

Tags

NGSS.HS-PS2-1

A rectangular rigid body consists of four spheres of equal mass connected by rods with negligible mass. The length of the long side of the rectangle is twice that of the short side. In Figure 1, the system is oriented as shown and rotates about the dashed axis that passes through the center of mass of the system. The rotational inertia about the axis is I1. In Figure 2, the system is turned 90° and rotates about the dashed axis shown that also passes through the center of mass of the system. The rotational inertia of the system about the axis is I2. Which of the following correctly compares I2 and I1?

• I2 > I1

• I2 < I1

• I2 = I1

• I2 is not comparable to I1

What is the average angular speed of the rod while it swings from -θ0 to θ0?

• θ0/Δt

• 2θ0/Δt

• θ0/(2Δt)

• Δt/θ0

Torque Test Review: What is the correct expression for angular displacement?

• 0

A wheel initially has angular speed ωᵢ when it begins to accelerate at a constant rate α, after which the wheel has angular speed ωf. Which of the following expressions is equal to the number of revolutions the wheel goes through while accelerating? Assume that the angular speeds are in rad/s and that the angular acceleration is in rad/s².

• (A) (ωf - ωᵢ) / 2πα

• (B) (ωf - ωᵢ) / α

• (C) (ωf² - ωᵢ²) / 4πα

• (D) (ωf² - ωᵢ²) / 2α

A student is provided with the data shown in the table for the angular speed of a wheel. Does the student have enough information to calculate the average angular acceleration of the wheel? Why or why not?

• Yes, because the average angular acceleration only depends on the change in angular speed and the time.

• Yes, because the angular acceleration only depends on the final values of the angular speed and the time.

• No, because the angular displacement needs to be known along with change in angular speed and time.

• No, because the initial direction of rotation must be known to calculate the change in the angular velocity.

A uniform rod is free to rotate about its left end, as shown. A force of magnitude F is exerted a distance d from the left end of the rod and at an angle θ = 90°. The force exerts a torque τ on the rod. Which of the following combinations of distance from the left end of the rod and angle θ would allow the force of magnitude F to exert the same torque τ on the rod?

• A: Distance = d/2, Angle = 30°

• B: Distance = d/2, Angle = 60°

• C: Distance = 2d, Angle = 30°

• D: Distance = 2d, Angle = 60°

Which of the following diagrams represents a system in rotational equilibrium?