A) 400\[\sqrt{3}\]m/s
B) 400 m/s
C) 400/\[\sqrt{3}\]m/s
D) 400\[\sqrt{2}\]m/s
Correct Answer: A
Solution :
KE lost by bullet = work done againes plank resistance \[\frac{1}{2}m{{v}^{2}}=Fx\] Here\[x\]is the distance pierced \[\frac{v_{2}^{2}}{v_{1}^{2}}=\frac{{{x}_{2}}}{{{x}_{1}}}\] \[\frac{v_{2}^{2}}{40000}=\frac{8}{6}\] \[{{v}_{2}}=\frac{400}{\sqrt{3}}m/s\]
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