Question

A moving body of mass m and velocity 3 km/h collides with a rest body of mass 2m and sticks to it. Now the combined mass starts to move. What will be the combined velocity

• A. 3 km/h
• B. 2 km/h
• C. 1 km/h
• D. 4 km/h

Answer 1

Answer: (C)

1 km/h

Answer 2

Initial momentum = $m \times 3 + 2 m \times 0 = 3 m$

Final momentum = $3 m \times V$

By the law of conservation of momentum

$3 m = 3 m \times V$⇒ $V = 1 \mathrm {~km} / \mathrm { h }$