Q20 of 46 Page 458

By what fraction does the mass of a boy increase when he starts running at a speed of 12 km h–1?

There is a physical significance of special theory of relativity that Energy and mass are interchangeable and that is given by Sir Einstein famous equation E=m

Gain in kinetic energy by the boy is possessed by the mass gain for the boy.



Given:


V=





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The energy from the sun reaches just outside the earth’s atmosphere at a rate of 1400 W m–2. The distance between the sun and the earth is 1.5 × 1011 m.

(a) Calculate the rate at which the sun is losing its mass.


(b) How long will the sun last assuming a constant decay at this rate? The present mass of the sun is 2 × 1030 kg.