Q. Two putty balls of equal mass moving with equal velocity in mutually perpendicular directions, stick together after collision. If the balls were initially moving with a velocity of $45\sqrt{2}\ ms^{- 1}$ each, the velocity of their combined after collision is
A) $45\sqrt{2}\ ms^{- 1}$
B) $45\ ms^{- 1}$
C) $90\ ms^{- 1}$
D) $22.5\sqrt{2}\ ms^{- 1}$
Explanation
(b) Initial momentum
$\overrightarrow{P} = m45\sqrt{2}\ \widehat{i} + m45\sqrt{2}\ \widehat{j}$
$\Rightarrow \left| \overrightarrow{P} \right| = m \times 90$
Final momentum $2m \times V$
By conservation of momentum
$2m \times V = m \times 90$
$\therefore V = 45\ m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.