Question

A steel ball of radius 2 cm is initially at rest. It is struck head on by another steel ball of radius 4 cm travelling with a velocity of 81 cm/s. If the collision is elastic their respective final velocities are

• A. 63 cm/s, 144 cm/s
• B. 144 cm/s, 63 cm/s
• C. 19 cm/s, 100 cm/s
• D. 100 cm/s, 19 cm/s

Answer 1

Answer: (B)

144 cm/s, 63 cm/s

Using mom. conservation
$81\times 8m=8m\times v_1+m\times v_2$
$648=8v_1+v_2$

& $e=\frac{v_2-v_1}{81}=1$

$v_2-v_1=81$
$\Rightarrow v_1=144$ cm/s
$v_2=63$ cm/s