(a) When the bob of pendulum is brought to a position making an angle $\theta$ with the equilibrium position, then height of fall of pendulum will be,
$h = l - l\cos\theta = l(1 - \cos\theta)$.
Taking free fall of the
$u = 0,\ a = g,\ g = h = l\left( 1 - \cos\theta \right),\ v = ?$
Now, $v^{2} = u^{2} + 2gh = 0 + 2gl\left( 1 - \cos\theta \right)$
or $v = \sqrt{2gl(1 - \cos\theta)}$