A boy of mass `60 kg` running at `3//s` jumps on to a trolley of mass `140 kg ` moving with a velocity of `1.5m//s` in the same direction . What is their common velocity?

Explanation

Here, `m_(1)=60 kg , u_(1) = 3m//s, m_(2)= 140 kg , u_(2) = 1.5m//s`
if `v` is their common velocity, then applying the principle of conservation of linear momentum, we get
`m_(1)u_(1)+m_(2)u_(2)= (m_(1)+m_(2))v` or `60xx3+140xx1.5= (60+140)v`
or `180+210= 200v` or `v=(390)/(200)= 1.95m//s`