An areoplane is flying horizontally with a velocity `720km//h` at a height of `2000 m`. When it is vertically at a point `A` on the ground, a bomb is released from it. The bomb strikes the gound at point `B`. The distance `AB` is

Options

A. `1 km`
B. `2 km`
C. `3 km`
D. `4 km`

Answer

D

Explanation

`u = 720 km//h = 720 xx (5)/(18) = 200 m//s`
`y = (g x^(2))/(2 u^(2))`
`x = sqrt((2 u^(2) y)/(g)) = sqrt((2(200)^(2) xx 2000)/(10))`
`AB = 4000 m = 4 km`
OR
`y = (1)/(2) g t^(2) rArr 2000 = (1)/(2) xx 10 xx t^(2) rArr t = 20 s`
`AB = x = u t = 200 xx 20 = 4000 m = 4 km`