A body is moving with a velocity v with respect to a frame of reference S1.
It bumps into a very heavy object and comes to rest instantaneously, its kinetic energy
12mv2
as seen from the frame S1 is completely converted to thermal energy.
Now, a man moving with a uniform velocity V (in the direction of the body) with respect to S1 observes the body. He notes that its initial kinetic energy of the body is
12m(v+V)2,
and that after it rams into the heavy body as
12mV2,
and concludes that the thermal energy produced is the difference
12m(v+V)2−12mV2 = 12mv2+mvV.
Which of the two answers is correct and why?
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