Question

A friction less pendulum of length 3 m swings with an amplitude of 10°. At its maximum displacement, the potential energy of the pendulum is 10 J. What is the kinetic energy of the pendulum when its potential energy is 5 J ? 

(A) 3.3 J 

(B) 5 J 

(C) 6.7 J 

(D) 10 J 

(E) 15 J

Answer 1

Correct option (B) 5J

At max displacement, the total energy is equal to the potential energy of 10J. Energy is conserved so when the K becomes 5J the U would have to be 5J also to conserve E.