A) 6 sec
B) 5 sec
C) 4 sec
D) 3 sec
Correct Answer: B
Solution :
The distance traveled in last second. \[{{S}_{\text{Last}}}=u+\frac{g}{2}(2t-1)\]\[=\frac{1}{2}\times 9.8(2t-1)\]\[=4.9(2t-1)\] and distance traveled in first three second, \[{{S}_{\text{Three}}}=0+\frac{1}{2}\times 9.8\times 9=44.1\ m\] According to problem\[{{S}_{\text{Last}}}={{S}_{\text{Three}}}\] \[\Rightarrow 4.9(2t-1)=44.1\Rightarrow 2t-1=9\] Þ t = 5 sec.
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