Consider a ball moving with a velocity of 10m/s and strikes a rough wall with the velocity with which it is moving at an angle of 37 degrees with the vertical and rebounds with same angle with 5m/s. Find the coefficient of friction of the wall.

the initial y-component of the ball = 8

initial x-component of the ball = 6

final y-component  = 4 

final x-component = 3

consider mass of ball as m 

now the momentum in x is changed by impulse of normal ( ∫Ndt )    (don''t be scared by the integration symbol , it''s just the denotion for impulse )

& the momentum in y by impulse of friction ( μ∫Ndt ) (since friction is kinetic )

now ,       ∫Ndt = 4m-8m = -4m

              μ∫Ndt = μ (-4m)= 3m-6m =-3m 

    therefore           μ = 0.75

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