A ball of mass `1 kg` strikes a heavy platform, 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

C

Explanation

As we know `e = [((v_(2) - v_(1)))/((u_(1) - u_(2)))]_(n)`

`1 = ((-5) - (v_(1)))/((10) - (-5)) implies v_(1) = - 20 m//s`
Hence ball will start moving towards upward direction with velocity `20 m//s`.
Let impulse imparted by plate force on the ball is `j` in upward direction.
`m u_(1) - J = - mv_(1)`
`implies J = m(u_(1) + v_(1)) = 1 (10 + 20) = 30 kg m//s`