Question

A frictionless pendulum of length of 3 m swings with an amplitude of 10o. 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. 5 J b. 10 J c. 15 J d. 3.3 J e. 6.7 J

Answer 1

Option A is the correct answer.

Explanation:

For a simple pendulum we have at any position

             Total energy = Constant        

             Kinetic energy + Potential energy = Constant

At maximum displacement of pendulum, velocity is zero, hence kinetic energy is zero.

At maximum displacement the pendulum only have potential energy.

Given that maximum potential energy is 10 J.

 That is at any position                

                     Kinetic energy + Potential energy = 10 J

Now we need to find kinetic energy when potential energy is 5 J.

                     Kinetic energy + 5 J = 10 J

                     Kinetic energy = 5 J

Option A is the correct answer.