A) \[14m{{s}^{-1}}\]
B) \[20m{{s}^{-1}}\]
C) \[28m{{s}^{-1}}\]
D) \[10m{{s}^{-1}}\]
Correct Answer: B
Solution :
Suppose a ball rebounds with speed \[v=\sqrt{2gh}=\sqrt{2\times 10\times 20}=20m/s\] Energy of a ball just after rebound, \[E=\frac{1}{2}m{{v}^{2}}=200m\] As 50% of energy loses in collision means just before collision energy is 400 m. According to law of conservation of energy we have \[\frac{1}{2}mv_{0}^{2}+mgh=400m\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\frac{1}{2}mv_{0}^{2}+m\times 10\times 20=400m\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{v}_{0}}=20m/s\]You need to login to perform this action.
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