It is a common observation that rain clouds can be at about 1 km altitude above the ground. If a rain drop falls from such a height freely under gravity, then what will be its speed in km `h^(-1)`?
(Take g = `10 m s^(-2)`)

Options

A. 510
B. 610
C. 710
D. 910

Answer

A

Explanation

Here, u = 0, g = `10 m s^(-2)`, h = 1 km = 1000 m
As `v^(2) - u^(2) `= 2gh = `therefore v^(2) = 2gh`
or v = `sqrt 2gh = sqrt 2 xx 10 xx 1000 = 10 sqrt 2 m s^(-1)`
= `100sqrt 2 xx 18/5 km h^(-1) = 360sqrt 2 km h^(-1) congto 510 km h^(-1)`