3. Two people are standing on a 2.0-m long stationary platform, one on each end.

Question

3. Two people are standing on a 2.0-m long stationary platform, one on each end. The platform floats parallel to the ground on a cushion of air, like a hovercraft. One person throws a 6.0-kg ball to the other, who catches it. The ball travels nearly horizontally. Excluding the ball, the total mass of the platform and people is 118 kg. Because of the throw, the 118-kg mass recoils. How far does it move before coming to rest again?

Explanation / Answer

net force on the system =0 momentum conserved before = after {M, V} = mass & speed of platform [118, V(recoil)] [m, v] = mass & speed of ball =[6, v] initial momentum =0 = final momentum 0 = mv + MV(recoil) ----------- (1) upon catching, platform will stop recoiling as air stiring will take place during that time only ------------------------ D = platform length = 2 m time taken >> t = D/v (for ball) = d / V(recoil) for platform d = platform recoil distance = [V(recoil) / v] D using (1) d = [m/M] D = [6*2/118] = 0.1017 meter

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