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A body is kept on top of a hill of height 'h'. If we fix the 0 potential energy at the ground, the body has an initial energy - mgh. Assume that the hill surface + ground is frictionless. When the body starts sliding (with negligible push), it gains a velocity of v=(2gh)

^{1/2}on reaching the ground, which follows from energy conservation.

Now suppose we observe the whole situation from a reference frame moving with a uniform velocity v=(2gh)

^{1/2}on the ground. Initially, the body has a total energy given by 0.5mv

^{2}+ mgh. On reaching the bottom, the total energy is 0!

Where does the energy vanish?