A) 6 s
B) 5 s
C) 7s
D) 4s
Correct Answer: B
Solution :
Given that the stone falls from rest, hence \[u=0.\]Now, distance covered in the last second is equal to distance covered in the first three seconds of the motion. Hence, \[{{S}_{3}}={{S}_{t}}\] \[\Rightarrow \] \[{{S}_{3}}=0+\frac{1}{2}g{{t}^{2}}=\frac{1}{2}\times 10\times 9=45\] and so, \[{{S}_{t}}=45=u+(2t-1)10/2\] \[\Rightarrow \] \[0+5(2t-1)=45\] \[\Rightarrow \] \[t=5s\]You need to login to perform this action.
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