Q8 of 13 Page 134

A running man has half the kinetic energy that a boy half his mass has. The man speeds up by 1.0ms–1 and then has the same energy as the boy. What were the original speed of the man and the boy?

Let,

M = mass of man


m = mass of boy


given, M = 2m


initially,


K1 = kinetic energy of man


K2 = kinetic energy of boy


u1 = speed of man


u2 = speed of boy


Given,





So,



Using






When the speed of man is increased by 1 ms–1, the kinetic energies of man and boy becomes equal.



Using,



We get,






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