A man standing on a road has to hold his umbrella at `30^(@)` with the vertical to keep the rain away. He throws the umbrella and starts running at `10 kmh^-1` He finds that raindrops are hitting his head vertically. The actual speed of raindrops is

Options

A. `20kmh^-1`
B. `10sqrt3 kmh^-1`
C. `20 sqrt3 kmh^-1`
D. `10kmh^-1`

Explanation

For a body projected,
The angle of projection `theta=30^(@)`
Range, R=20m
Considering Range equation
`R=(u^2sin2theta)/g=(u^2sin(2xx30))/g`
`u^2/g=20/(sin60^(@))=20/(sqrt3/2)=40/sqrt3`
maximum height,
`H=(u^2sin^2theta)/(2g)=1/2xx40/sqrt3xxsin30^(@)=5/(sqrt3m)`