Total Energy of an Simple Harmonic Motion is given as
1/2m(wA)^2
Kinetic energy for any Simple Harmonic Motion can be written as
1/2 m(wA)^2 cos^2(wt).
so for 75% KE,
3/4 * 1/2 m(wA)^2=1/2 m(wA)^2 cos^2(wt)
=> ((3)^1/2)/2=cos(wt)
we get , wt = pi / 6
w=2 pi/T
t=T/12 = 1/6 seconds.
So the answer is 1/6 seconds
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