A) 1.5 s
B) 4.025 s
C) 5.4 s
D) 6.75 s
Correct Answer: C
Solution :
\[\operatorname{h}=ut+\frac{1}{2}\,g{{t}^{2}}\] \[\Rightarrow \,\,\,-81+0.5\times 10\times {{t}^{2}}\,\,\Rightarrow \,\,5.4\,sec\] \[\operatorname{Acceleration} = \frac{dv}{dt} = \frac{(60-20)}{0.25} = 160\,\,km/ {{h}^{2}}\]
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