Two balls are dropped to the ground from different heights. One ball is dropped 2 s after the other but they both strike the ground at the same time. If the first ball takes 5 s to reach the ground, then the difference in initial heights is (Take `"g = 10 m s"^(-2)`)

Options

A. 20m
B. 80m
C. 170m
D. 40m

Answer

B

Explanation

When `t_1 = 5 sec`
`h_1 = 1/2 g t_1^2 = 1/2 xx 10 xx 25 = 125m`
when `t_1 = 3sec`
when `t_2 = 3 sec`
`h_2 = 1/2 xx 10 xx 9 = 45m`