A simple pendulum of length l is pulled aside to make an angle $\theta$ with the vertical. What is the magnitude of the torque of the weight of the bob about the point of suspension ?

$\begin {array} {1 1} (a)\;mg \sin \theta l & \quad (b)\;mg \cos l \\ (c)\;mgl & \quad (d)\;mg l/2 \sin \theta \end {array}$

z= Force $\times$ perpendicular distance of the force from the axis of rotation .
Hence a is the correct answer.

edited Jan 25, 2014 by meena.p