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)

45

Answer 2

Initial momentum
$\vec{P} = m45\sqrt{2} \hat{i} + m45\sqrt{2} \hat{j}$
$\Rightarrow\quad\left|\vec{P}\right| = m\times90$
Final momentum 2m ? V
By conservation of momentum
2m ? V = m ? 90
$\therefore$ V = 45 m/s

So, the correct option is(B): 45.