Question

A moving mass of 8 kg collides elastically with a stationary mass of 2 kg. If E be the initial kinetic energy of the mass, the kinetic energy left with it after collision will be

• A. 0.80 E
• B. 0.64 E
• C. 0.36 E
• D. 0.08 E

Answer 1

Answer: (C)

0.36 E

Answer 2

Kinetic energy retained by projectile

$\frac{\Delta K}{K} = \left( \frac{m_{1} - m_{2}}{m_{1} + m_{2}} \right)^{2}$

⇒ $\Delta K = \left( \frac{8 - 2}{8 + 2} \right)^{2}E$ =$= \frac{9}{25}E = 0.36E$.