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, the common velocity if it is perfectly inelastic collision

• A. 144cm/s
• B. 61 cm/s
• C. 81 cm/s
• D. 72cm/s

Answer 1

The correct option is D 72cm/s

8m since mass is propotional to $r^3$
Momentum conservation
$8m\times 81=9\times v$
$v=72$ cm/s