A truck of mass `2500 kg` moving at `15m//s` collides with a car of mass `1000kg` moving at `5m//s` in the opposite direction . With what velocity would the two move together?

Explanation

Here, `m_(1)= 2500 kg , u_(1)= 15m//s, m_(2)=1000kg , u_(2)= -5m//s`
Negative sign with `u_(2)` indicates that `u_(2)` is in a direction opposite to `u_(1)`.
If `v` is the combined velocity of the two, 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 `2500xx15+1000(-5)=(2500+1000)v`
or `37500-5000= 3500v` or `v=(32500)/(3500)= 65/7= 9.3m//s`
Positive sign of `v` indiacates that the resultant velocity is in the direction of motion of the truck.