A body of mass `50 kg` is projected vertically upward with velocity of `100 m//s`. After `5 s` this body breaks into `20 kg` and `30 kg`. If the `20 kg` piece travels upwards with `150 m//s`, then the velocity of other block will be

Options

A. 15 m/sec downwards
B. 15 m/sec upwards
C. 51 m/sec downwards
D. 51 m/sec upwards

Answer

A

Explanation

Velocity after 5 sec –
`v=u -"gt" = 100 - 9.8 xx 5 = 51 m//s`
`mv = m_1 v_1 + mv_2`
`implies 51 xx50 = 20 xx 150 +30 xxv_2`
`implies v_(2) = (2500 - 3000)/(30) = (-450)/(30) = -15m//s`
(downward)