Question

a ball of mass g moving with 20m/s strikes a vertical wall and rebounds along the same line with a velocity of 15m/s .if the time of contact is 0.1s the force ecxerted by the wall on the ball is

Answer 1

m = 0.2 kg 
u = 30 m/s 
v =  20 m/s

impulse = change in the momentum 
             final momentum - initial momentum
             mv - mu
             m ( v - u )
        => 0.2 *  (-20 -30 )
             = -10 Ns