A ball dropped from the top of a tower covers a distance `7x` in the last second of its journey, where `x` is the distance covered in the first second. How much time does it take to reach to ground?.

Options

A. 3s
B. 4s
C. 5s
D. 6s

Answer

B

Explanation

distance covered in 1st is `x=(1)/(2)g(1)^(2)=(g)/(2)`
Let it falls for n sec then last sec is `n^(th)` sec.
`therefore 7x=0+(g)/(2)(2n-1)`
`rArr 7xx(g)/(2)=(g)/(2)(2n-1)`
`rArr 2n=8 rArr n=4` sec