A) 0.09 sec
B) 0.9 sec
C) 2.1 sec
D) 1.3 sec
Correct Answer: A
Solution :
\[v=\sqrt{2gh}\] \[=\sqrt{2\times 9.8\times 100}=14\sqrt{10}m/\sec \] Now, \[{{v}^{2}}={{u}^{2}}+2as\] \[\therefore \] \[0=(14\sqrt{10})2+2a\times 2\] \[\Rightarrow \] \[a=-490\,\,m/{{s}^{2}}\] Again, \[v=u+at\] \[\therefore \] \[0=14\sqrt{10}-490t\] \[\therefore \] \[t=\frac{14\sqrt{10}}{490}=\mathbf{0}\mathbf{.09}\,\,\mathbf{sec}\]
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