Question

The recoil velocity of a $ 4.0\, kg $ rifle that shoots a $ 0.050\, kg $ bullet at a speed of $ 280\text{ }m{{s}^{-1}} $ is:

• A. $ +3.5\text{ }m{{s}^{-1}} $
• B. $ -3.5\text{ }m{{s}^{-1}} $
• C. $ -\sqrt{(3.5)}\text{ }m{{s}^{-1}} $
• D. $ +\sqrt{(3.5)}\text{ }m{{s}^{-1}} $
• E. $ \text{+7 }m{{s}^{-1}} $

Answer 1

Answer: (B)

$ {{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}=0 $
$ \Rightarrow $ $ {{u}_{1}}=-\frac{{{m}_{2}}{{u}_{2}}}{{{m}_{1}}} $
$ =\frac{0.050\times 280}{4}=-3.5\,m{{s}^{-1}} $