## Problem Statement

**54) A boy of mass 50 kg running at 5 m/s jumps
on to a 20 kg trolley travelling in the same direction at 1.5 m/s. What is
their common velocity?**

## Solution

**Initial total momentum= (50 x 5 + 20 x 1.5 ) kg m/s = 280 kg m/s**

Final combined mass = (50+20) kg = 70 kg

Let the final velocity of the combined system = V

**According to the conservation of linear momentum:**** 70 V = 280 V = 280/70 = 4 m/s**

Question Set – Physics Problems for grade 9

Solution to problems – class 9 – Set 1 Q 54