Question

As a pendulum swings back and forth, its total energy is 16 J. What is its kinetic energy at 3/4 its maximum height?

A. 4
B. 5

Answer 1

So we can do the ratio ke/KE = (TE - mgh)/mgH where h = 3/4 H is given. Solve for ke, the kinetic energy when h = 3/4 H.

ke = KE (TE - mg 3/4 H)/mgH = KE (TE/mgH - mg 3/4 H/mgH) = KE (1 - 3/4) = KE/4. Thus the kinetic energy when at h = 3/4 H is 1/4 the KE at the bottom or 1/4 TE = 4 J. ANS.