Question

A uniform disk with mass m = 9.07 kg and radius R = 1.36 m lies in the x-y plane and centered at the origin. Three forces act in the +y-direction on the disk: 1) a force 313 N at the edge of the disk on the +x-axis, 2) a force 313 N at the edge of the disk on the –y-axis, and 3) a force 313 N acts at the edge of the disk at an angle θ = 31° above the –x-axis.

1)

What is the magnitude of the torque on the disk about the z axis due to F₁?

N-m

2)

What is the magnitude of the torque on the disk about the z axis due to F₂?

N-m

3)

What is the magnitude of the torque on the disk about the z axis due to F₃?

N-m

4)

What is the x-component of the net torque about the z axis on the disk?

N-m

5)

What is the y-component of the net torque about the z axis on the disk?

N-m

6)

What is the z-component of the net torque about the z axis on the disk?

N-m

7)

What is the magnitude of the angular acceleration about the z axis of the disk?

rad/s²

8)

If the disk starts from rest, what is the rotational energy of the disk after the forces have been applied for t = 1.8 s?

J

Answer 1

2) If the line of action of force passes through a point/axis then its torque about that point/axis is zero.

4) same reason as part 2)

5) if a force doesn't have a tendency of rotation about an axis then its torque about that axis is zero.