The mass of a pendulum bob is 0.2 kg, and it is suspended by a string 1 m long. It is pulled aside until the thread is at 30° to the vertical. How much work is done? The ball is now released. Find its K.E. at the lowest point? Take g = 10 ms^–2.

Here,  m = 0.2kg, OA = OB = 1m,

∠AOB = θ = 30°.

From B, draw  BC ⊥ OA,

In ΔBOC,   cosθ =OC/OB

OC = OB cosθ

= 1 cos 30° =√3/2

= 0.866m

Height through which bob is raised

= AC = OA − OC

= 1 − 0.866 = 0.134m

Work done = mgh

= 0.2 × 10 × 0.134 = 0.268J

K.E. at the lowest point = work done

= 0.268J.