A) 0.12s
B) 0.08 s
C) 0.04 s
D) 12 s
Correct Answer: A
Solution :
Velocity by which the ball hits the bat \[{{v}_{1}}=\sqrt{2g{{h}_{1}}}=\sqrt{2\times 10\times 5}\]or \[\overrightarrow{{{v}_{1}}}=+10\,m/s=10\,m/s\] velocity of rebound \[{{v}_{2}}=\sqrt{2g{{h}_{2}}}=\sqrt{2\times 10\times 20}=20\,m/s\] or \[\overrightarrow{{{v}_{2}}}=-20\,m/s\] \[F=m\frac{dv}{dt}=\frac{m(\overrightarrow{{{v}_{2}}}-\overrightarrow{{{v}_{1}}})}{dt}=\frac{0.4(-20-10)}{dt}=100\,N\] by solving \[dt=0.12\,\sec \]
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