Question

A pendulum of length 50 cm is pulled 30 cm away from the vertical axis and released from rest. What will be its speed at the bottom of its swing

Answer 1

m g h = 1/2 m v^2 potential energy will be converted to kinetic energy

h = h0 (1 - cos theta) where theta is the displacement

theta = 30 / 50 = .6 theta = 36.9 deg

v^2 = 2 g h from above

h = 50 (1 - cos 36.9) = 50 * .2 = 10 cm

v = (2 * 980 * 10)^12 = 140 cm/sec