Two identical balls are shot upward one after another at an interval of 2s along the same vertical line with same initial velocity of `40 ms^-1`. The height at which the balls collide is

Options

A. `120 m`
B. `75 m`
C. `200 m`
D. `45 m`

Answer

B

Explanation

u=40 m/s , `g=10 m//s^(2)`
Let t be time taken by the first ball to reach the highest point.
`V=-u-g t " " O=40-10 t " " t= 4s`
After reaching the first ball at the highest point now, both the balls will collide after 1 sec as both the balls therefore, the height of collision point =height gained by the second ball in 3 sec