A ball of mass 1.74 kg is dropped from a height y1 = 1.47 m and then bounces back up to a height of y2 = 0.83 m. How much mechanical energy is lost in the bounce? The effect of air resistance has been experimentally found to be negligible in this case, and you can ignore it.

ΔE = mgΔy =mg(y1-y2).