The bob of a pendulum of length l is pulled aside from its equilibrium position through an angle θ and then released. The bob will then pass through its equilibrium position with a speed v, where v equals

If suppose bob rises up to a height h as shown then after releasing potential energy at extreme position becomes kinetic energy of mean position⇒mgh=12mvmax2⇒vmax=2ghAlso, from figure cosθ=l−hl⇒h=l(1−cosθ)So, vmax=2gl(1−cosθ)