A ball of mass `1 kg` strikes a heavy plarform elastically, moving upwards with a velocity of `5 m//s` . The speed of the ball just before the collision is `10 m//s` downwards. Then the impulse imparted by the platform on the ball is

Options

A. `15 N-s`
B. `10 N-s`
C. `20 N-s`
D. `30 N-s`

Answer

D

Explanation

`e = - ((v_(2) - v_(1))/(u_(2) - u_(1))) rArr 1 = - (5 - v_(1))/(5 - (-10)) = (v_(1) - 5)/(15)`
`rArr v_(1) = 20 m//s`
`:.` Impulse on ball `= m(vec(v) - vec(u)) = 1 xx [20 -(10)] = 30N-s`