Question

Two putty balls of equal masses moving with equal velocity in mutually perpendicular directions, stick together after collision. If the balls were initially moving with a velocity of $45\sqrt{2}m{s}^{-1}$ each, the velocity of their combined mass after collision is

• A. $45\sqrt{2}m{s}^{-1}$
• B. $45m{s}^{-1}$
• C. $90m{s}^{-1}$
• D. $22.5\sqrt{2}m{s}^{-1}$

Answer 1

The correct option is B

$45m{s}^{-1}$

Initial momentum

$\overrightarrow{P}=m45\sqrt{2}\hat{i}+m45\sqrt{2}\hat{j}\Rightarrow |\overrightarrow{P}|=m\times 90$

Final momentum = 2mV

By conservation of momentum $2m\times V=m\times 90$

$\therefore$ V = 45 m/s