Question

A ball A of mass 2.5kg moving at 5 m/s collides with an identical ball B at rest. A stops and B starts moving. What is the magnitude of velocity of B after the collision?

• A. 5 m/s
• B. 12.5 m/s
• C. 2.5 m/s
• D. 10 m/s

Answer 1

Answer: (A)

5 m/s

Given :

$m_A=m_B=2.5$ kg

$u_A=5$ m/s

$u_B=0$ m/s

$v_A=0$

Conservation of momentum:

Intial momentum $=$ Final momentum

$m_A{u}_A+m_B{u}_B=m_A{v}_A+m_B{v}_B$

$\therefore$ $2.5\left(5\right)+0=0+2.5v_B$

$⟹v_B=5$ m/s