How Is Power Extracted from Wind Turbines?

[Pseudopro]

Homework Statement

Air of density 1.2kgm^-3, speed 8ms^-1 is incident on blades of wind turbine. Radius of blades 1.5m. After passing blades, wind speed is reduced to 3.0ms^-1 and density 1.8kgm^-3. How much power is extracted from wind?

Homework Equations

P=1/2 pAv³

The Attempt at a Solution

P=1/2 x 1.2 x pi x 1.5²x 8³. But I don't know what to do with the information about the wind after passing blades.

 

[Pseudopro]

I've solved it - thank you for your time :)

 

[engrbilal876]

How to calculate surface area of wind turbine blade

i want to calculate surface area of wind turbine blade,

can anyone help me out,any formula or software for it?