A) \[5\sqrt{3}\,m/s\]
B) \[10\sqrt{3}\,m/s\]
C) \[10\sqrt{6}\,m/s\]
D) \[10\sqrt{2}\,m/s\]
Correct Answer: C
Solution :
Let the speed of projection be \[u=10\sqrt{2}\,m/s\]and the speed of the ball just before hitting the ground be v. Applying law of conservation of mechanical energy, we get: \[\frac{1}{2}m{{u}^{2}}+mgh=\frac{1}{2}m{{v}^{2}}\] \[\therefore \] \[v=\sqrt{{{u}^{2}}+2gh}\] \[=\sqrt{200+2\times 10\times 20}\] \[=\sqrt{600}=10\sqrt{6}\,m/s\] Hence, the correction option is [c].
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