Question

A trolley of mass 4kg moving on smooth horizontal platform with a speed of 1.0m\s collide perfectly with a stationary trolley of same mass in the same platform. Calculate in total momentum of the two trolley immediately after the collision

Answer 1

The law of conservation of momentum states

$$p_{initial}=p_{final}$$

So, the total momentum

$$p=mv=4\:\rm kg\times 1.0\:\rm m/s=4\: kg\cdot m/s$$