A) \[14\,\,m{{s}^{-1}}\]
B) \[20\,\,m{{s}^{-1}}\]
C) \[28\,\,m{{s}^{-1}}\]
D) \[10\,\,m{{s}^{-1}}\]
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 |
| \[\frac{1}{2}mv_{0}^{2}+mgh=400m\] |
| \[\Rightarrow \] \[\frac{1}{2}mv_{0}^{2}+m\times 10\times 20=400m\] |
| \[\Rightarrow \] \[\,{{v}_{0}}=20m/s\] |
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