Question

A ball of mass 0.50kg moving at a speed of 5.0 m/s collides with another ball of mass 1.0kg. After the collision the balls stick together and remain motionless. Waht was the velocity of the 1.0 kg block before the collision?

• A. 0 m/s,at rest
• B. 2.5 m/s ,in same direction of first ball
• C. 3.5 m/s ,in opposite direction of first ball
• D. 2.5 m/s , in opposite dirction of first ball

Answer 1

The correct option is D 2.5 m/s , in opposite dirction of first ball

Mass of the ball $=m_1$ = 0.5kg, velocity of the ball = 5m/s
Mass of the another ball $m_2=1kg$
Let it's velocity = v' m/s
Using law of conservation of momentum,
$0.5\times 5+1\times v^{\prime }=0\Rightarrow v^{\prime }=-2.5$
$\therefore$ Velocity of second ball is 2.5m/s opposite to the direction of motion of $1^{st}$ ball.