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Question

A running man has half the kinetic energy of that of a boy of half of his mass. The man speeds up by 1 m/s so as to have same K.E. as that of boy. The original speed of the man will be



A

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B

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C

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D

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Solution

The correct option is C


Let m = mass of the boy, M = mass of the man, v = velocity of the boy and V = velocity of the man

Initial kinetic energy of man = 12MV2=12[12mv2]=12[12(M2)v2][As m=M2given] V2=v24V=v2   ....(i)

When the man speeds up by 1 m/s, 12M(V+1)2=12mv2=12(M2)v2(V+1)2=v22V+1=v2   (ii)

From (i) and (ii)  we get speed of the man V=121m/s.


Physics

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