Suppose the average mass of raindrops is `3.0xx10^(-5)kg` and their average terminal velocity `9ms^(-1)`. Calculate the energy transferred by rain to each square metre of the surface at the place which receives 100 cm of rain in a year.

Options

A. `23.5 xx 10 ^(5)J`
B. `4. 05 xx 10 ^(4) J`
C. `3. 0 xx 10 ^(5) J`
D. `9.0 xx 10 ^(4) J`

Answer

B

Explanation

Total volume of rain drops, received 100 cm in a year by area `1 m ^(2) = 1m^(2) xx (100)/( 100) m = 1 m ^(2)`
As we know, density of water, `f = 10 ^(3) kg//m^(3)`
Therefore, mass of this volume of water
` M = d xx v = 10 ^(3) xx 1 = 10 ^(3) kg`
Average terminal velocity of rain drop
`v = 9 m//s` (given)
Therefore, energy transferred by rain,
`E = 1/2 mv ^(2) = 4. 05 xx 10 ^(4) J`