Question

A bullet is fired from a rifle and the rifle recoils. Kinetic energy of rifle is

• A. less than K.E. of bullet
• B. greater than K.E. of bullet
• C. equal to K.E. of bullet
• D. none of the above

Answer 1

Answer: (B)

greater than K.E. of bullet

Answer 2

Momentum of rifle = Momentum of bullet $m_{1} v_{1}=m_{2} v_{2}$, Also $m_{1} >m_{2}$ $\frac{\text { K.E. of rifte }}{\text { K.E. of bullet }}=\frac{\frac{1}{2} m_{1} v_{1}^{2}}{\frac{1}{2} m_{2} v_{2}^{2}}$ $=\frac{m_{1}^{2} v_{1}^{2}}{m_{1}} \frac{m_{2}}{m_{2}^{2} v_{2}^{2}}=\frac{m_{2}}{m_{1}}$ K.E. of rifle is less than $K . E$. of bullet.