MHTCET 2016 Physics Solved Paper

(c) Potential energy of pendulum, when bob is at rest, is given by
(PE) = mgl
When bob is displaced by small angular displacement 0, the pendulum will lose PE of bob which gets converted into kinetic energy (KE). So, from conservation of energy
Loss in PE = gain in KE
KE = mgI - mgI cos θ = mgl (1 - cos θ)