A stone falls from rest. The total distance covered by it in the last second of its motion is equal to the distance covered by it in the first three seconds of its motion. How long does the stone remain in air?

Options

A. 4 s
B. 5 s
C. 6 s
D. 7 s

Answer

b

Explanation

Let the stone remain in air for n seconds then the distance covered in nth second `x=0+(10)/(2)(2n-1)` or x=10n-5: Also the distance covered in first three second is
`=0+(1)/(2)xx10xx9=45`
`:.10n -5 5=45` or n=5 seconds