Question

A pendulum bob of mass m on a cord of length L is pulled sideways until the cord makes an angle θ with the vertical as shown in the figure to the right. The change in potential energy of the bob during the displacement is: 

(A) mgL (1–cos θ) 

(B) mgL (1–sin θ) 

(C) mgL sin θ 

(D) mgL cos θ 

(E) 2mgL (1–sin θ)

Answer 1

Correct option (A) mgL (1–cos θ)

   

The potential energy at the first position will be the Lcos θ amount “lost” as the ball falls and this will be the change in potential. 

U= mgh = mg(L– Lcosθ)