This problem follows up on a discussion from lecture. A wind turbine with an efficiency of 45% for converting wind energy into electrical energy is designed to yield 10 kW of electrical power in a 20 mi/h wind. [The density of air is 1.2 kg/m3.]

What length rotor blades does this wind turbine have?

4.1 m

Explanation:

10 kW = 10000 W

20mi/h = 20*1.6 km/mi = 32 km/h = 32 * 1000 (m/km) *(1/3600) hr/s = 8.89 m/s

The power yielded by the wind turbine can be calculated using the following formula

where is the air density, v = 8.89 m/s is the wind speed, A is the swept area and is the efficiency

The swept area is a circle with radius r being the blade length

close lines strong magnet less close weaker

no simpler subs form complex ones. synthesise = make