Q11 of 35 Page 143

N balls each of mass m impinge elastically in each second on a surface with velocity u. The average force experienced by the surface will be?



Mass of each ball = m kg


Velocity = u m/s


This is the case of elastic collision where momentum is conserved.


Change in momentum = mu – (–mu)


= 2mu


For N balls


dp = N × 2mu


= N2mu


Rate of change in momentum = dp/dt


= 2Nmu/1


= N2mu


According to Newton's Second Law


= Energy = dp/t


= N2mu


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