Chapter 29, Problem 76E

(a)

To determine

The net torque that acts on the loop when it has rotated through an angle $\varphi$ from its original orientation and is rotating downward at an angular speed $\omega$.

(b)

To determine

The angular acceleration of the loop.

(c)

To determine

whether it takes the loop a longer or shorter time to rotate through $90°$ and explain the reason.

(d)

To determine

Whether mechanical energy conserved as the loop rotates downward and explain the reason.