Question

Two balls each of mass 0.25 kg are moving towards each other in a straight line, one at 3 ms${}^{-1}$ and the other at 1 ms${}^{-1}$ collide. The balls stick together after the collision. The magnitude of the final velocity of the combined mass is :

• A. 1/2 ms${}^{-1}$
• B. 1 ms${}^{-1}$
• C. 2 ms${}^{-1}$
• D. 4 ms${}^{-1}$

Answer 1

Answer: (B)

1 ms${}^{-1}$

Here, two balls each of mass 0.25 kg are moving towards each other than in a straight line, one at $3m{s}^{-1}$ and the other at $1m{s}^{-1}$ collide and the balls stick together after the collision, hence
$m_1{u}_1-m_2{u}_2=(m_1+m_2)v$
$\left(0.25\right)\left(3\right)-\left(0.25\right)\left(1\right)=(0.25+0.25)v$
$\left(0.75\right)-\left(0.25\right)=\left(0.5\right)v$
$v=1m{s}^{-1}$