### Solution to problems – class 9 – Set 1 Q 56

##### July 1, 2019

## Problem Statement

**56)A truck of mass 500 kg moving at 4 m/s collides with another truck of mass 1500 kg moving in the same direction at 2 m/s. ****What is their common velocity just after the collision if they move off together?**

## Solution

Total initial momentum = 500 x 4 + 1500 x 2 = 5000 kg m/s

Now after collision as they combine, their net mass is =500 +1500 =2000 kg

Let the common velocity is V

So final momentum is 2000V

As per law of conservation of momentum

2000 V = 5000

So V = 5000/2000 m/s = 2.5 m/s