Answer:
(a)
(i) A cricket/hockey ball which has been hit hard and is travelling fast.
(ii)A shot put thrown by an athlete
(b) Let the body of mass m at height h above the ground
starting from rest, be falling freely.
Total energy of the body at height h
= mgh (PE) + 0 (KE) = mgh
After the body has fallen freely through a distance x
(say), K.E. = mgh, P.E. = mg (h-x)
Work and Energy 135
Total energy = K.E. + P.E.
= mgh + mg (h - x) = mgh
When it reaches the ground
P.E. = 0, Total Energy = K.E. + P.E. = mgh
Thus, the total mechanical energy, which is the sum of
K.E. and P.E. is always equal to mgh.
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