A particle executes simple harmonic motion with a frequency f. The frequency with which its kinetic energy oscillates is
f2
f
2f
4f
Kinetic energy K = 12mv2 = 12ma2ω2 cos2 ωt = 12mω2a2(1+cos 2ωt) hence kinetic energy varies periodically with double the frequency of S.H.M. i.e., 2f.