Question

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 $45\sqrt{2}$ m/sec each, the velocity of their combined mass after collision is (in m/sec).

• A. $45\sqrt{2}$
• B. 45
• C. 90
• D. $22.5\sqrt{2}$

Answer 1

Answer: (B)

Initial momentum
$\vec{P}=m45\sqrt{2}\hat{i}+m45\sqrt{2}\hat{j}$
$\Rightarrow \left|\vec{P}\right|=m\times 90$
Final momentum 2m × V
By conservation of momentum
2m × V = m × 90
$\therefore$ V = 45 m/s