A) \[4\,\,mnu\]
B) \[2\,\,mnu\]
C) \[1.5\,\,mnu\]
D) \[0.8\,\,mnu\]
Correct Answer: B
Solution :
Key Idea : Force experienced by the surface is equal to change in momentum in one second. From Newton's second law of motion the rate of change of momentum of a body is equal to the external force applied on the body and the change is momentum always takes place in the direction of the force. Momentum of ball before inpact = mu Momentum after inpact = - mu Change in momentum = mu - (- mu) = 2 mu. Change in momentum due to n balls in one second is = 2 mnu. Change of momentum = Force experienced per second = 2 mnu.
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