The blades of a windmill sweep out a circle of area A
Assume that the windmill converts `25%` of the wind's energy into electricla energy and that `A = 30m^(2) `, v = 36 km/ h and the density of air 1.2 kg `m^(-3)` . What is the electrical power produced ?

Explanation

Electrical energy produced `= ((25)/(100)) xx `K.E
of air `= (1)/(4) xx (1)/(20 xx Av^(3) rho t`
Electrical power `= (1)/(8) (Av^(3) rho t)/( t) = (1)/(8) Av^(3) rho t`
`P = (1)/(8) xx 30 xx (10)^(3) xx 1.2 = 4500 ` watt = 4.5 Kw