Question

A pendulum consists of a ball of mass m suspended at the end of a mass less cord of length L as shown. The pendulum is drawn aside through an angle of 60° with the vertical and released. At the low point of its swing, the speed of the pendulum ball is 

(A) √gL 

(B) √2gL 

(C) ½gL 

(D) gL 

(E) 2gL 

Answer 1

Correct option  (A) √gL 

Use energy conservation, U top = K bottom. As in problem #6 (in this document), the initial height is given by L – Lcos θ, with cos 60 = .5 so the initial height is ½ L.