Here's the question you clicked on:
adnanchowdhury
Kinetic Energy and Potential Energy question: http://d.pr/i/vcK4 The gymnast descends from position B and regains contact with the trampoline when it is in its unstretched position. At this position, her centre of mass is 3.2 m below its position at B. Calculate her kinetic energy at the instant she touches the unstretched trampoline
nope. That's PE of when the person is at B.
and i will be ke once the person reaches back
kinetic energy =3.2/4.2 *2264
@lalaly: Wow...that's much more shorter than the stuff I was about to post but it's dead-on.
Well, almost :) (3.2/4.2)*2264
At any rate, what lalaly did was calculate the total PE from point A to B given 4.2m, 55kg and g (mgh = 2264J). Her KE at point B will be equal to this. Once you know those two things, you should be able to see that (3.2/4.2)*2264J will be the amount of KE at the point where the girl just touches the unstretched trampoline.