Q. A 20 kg ball moving with a velocity $6\ {ms}^{- 1}$ collides with a 30 kg ball initially at rest .if both of them coalesce ,then final velocity of the combined mass is
A) $6\ ms^{- 1}$
B) $5\ ms^{- 1}$
C) $3.6\ ms^{- 1}$
D) $2.4ms^{- 1}$
Explanation
(d) From conservation of momentum.
Momentum before collision =Momentum after collision
$m_{1}u_{1} + m_{2}u_{2} = m_{1}v_{1} + m_{2}v_{2}$
20$\times 6 + 30 \times 0 = 20v + 30v$
$\therefore 20 \times 6 = 50v$
Or $v = \frac{120}{50} = 2.4ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.