A man throws a ball at an angle of `45^@` with the horizontal plane from a height of 15 m. If the shot strikes the ground at a horizontal distance of 30 in, the velocity of throw is (Take `g=10 m s^(-2)`)

Options

A. 10 m `s^(-1)`
B. `10 sqrt2 m s^(-1)`
C. `20 m s^(-1)`
D. `20sqrt2 m s^(-1)`

Answer

B

Explanation

For horizontal motion, `x=u cos theta t`
so, `30=u cos 45^@ t = u/sqrt2t` …(i)
For vertical downward motion , -y=u sin `45^@ t -1/2 g t^2`
or `-15=u/sqrt2 t- 1/2 xx 10 xx t^2` or t=3s (Using (i))
`therefore` Velocity of the throw , `u=(30sqrt2)/t=10sqrt2 m s^(-1)`