An object fallen freely from top of tower reaches at ground in 4s, then find the height of tower. (Take `g = 10 ms^(-2)`)

Options

A. 20 m
B. 40 m
C. 80 m
D. 160 m

Answer

C

Explanation

For object falling freely,
`d = v _(0)t + (1)/(2) g t^(2)`
`d = 1/2 g t ^(2) (v _(0) =0 and a =g)`
`therefore d = 1/2 (10) (4) ^(2) = 80m`