A projectile is projected at `10 ms^(-1)` by making at an angle `60^(@)` to the horizontal. After some time its velocity makes an angle of `30^(@)` to the horizontal. Its speed at this instant is

Options

A. `(10)/(sqrt(3))`
B. `10 sqrt(3)`
C. `(5)/(sqrt(3))`
D. `5 sqrt(3)`

Answer

A

Explanation

Let v be the velocity of the projectile at P when it makes an angle `30^(@)` with the horizontal.
Then
`v cos 30^(@) = u cos 60^(@) = 10 xx (1)/(2)` = 5
`v = (5)/( cos 30^(@)) = (5)/(sqrt(3)/2) = (10)/(sqrt(3)) m s^(-1)`