Question

A simple of length is pulled aside to make an angle θ with the vertical. Find the magnitude of the torque of the weight w of the bob about the point of suspension. When is the torque zero?

Answer 1

A simple of pendulum of length l is suspended from a rigid support. A bob of weight W is hanging on the other point. When the bob is at an angle θ with the vertical, 

then total torque acting on the point of suspension = i = F × r

⇒ W r sin θ  = W l sin θ

At the lowest point of suspension the torque will be zero as the force acting on the body passes through the point of suspension.