A) \[2.2\times {{10}^{3}}N\]
B) \[3.2\times {{10}^{3}}N\]
C) \[4.2\times {{10}^{3}}N\]
D) \[5.2\times {{10}^{3}}N\]
Correct Answer: D
Solution :
Key Idea: Kinetic energy of bullet is used in doing work against resistance offered by wood. The bullet moving with velocity v and having mass m, possesses kinetic energy given by \[K=\frac{1}{2}m{{v}^{2}}\] Given, \[m=20\,g=20\times {{10}^{-3}}kg,\,v=250\,m/s\] \[K=\frac{1}{2}\times 20\times {{10}^{-3}}\times {{(250)}^{2}}\] \[K=625\,J\] This energy is used in doing work against resistance offered by wood. Also, work done = force [F] \[\times \]displacement (d) \[\therefore \] \[625=F\times 12\times {{10}^{-2}}\] \[\Rightarrow \] \[F=\frac{625}{0.12}=5.2\times {{10}^{3}}N\]
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