Chapter 12 - Exercises and Problems - Page 214: 16

(a) $\tau=(\frac{L}{2})mg$ (b) 0 (c) $\tau=(\frac{L}{4})mg$

We know that (a) $\tau=r\times F$ $\implies \tau=(\frac{L}{2})mg$ (b) $\tau=r\times F$ $\implies \tau=(0)mg$ $\tau=0$ (c) $\tau=r\times F$ $\implies \tau=(\frac{L}{4})mg$