3. Consider a large windmill 30m in diameter. On a windy day, suppose that the windmill entrains a stream of air at a speed of 40 mph. Downstream of the windmill, the entrained stream exits over a large diameter at a speed of 20 mph. The pressure is 2atm at the inlet and equals atmospheric pressure at the outlet. Find the power (in megawatts) generated by the windmill. Density of air is 1.2 kg/m3

The power generated by the windmill is approximately 1.364 MW

Explanation:

The diameter of the windmill, d = 30 m

The inlet speed of the wind, = 40 mph = 17.88 m/s

The exit stream velocity, = 20 mph = 8.94 m/s

The pressure at the inlet, P₁ = 2 atm

The pressure at the outlet, P₂ = 1 atm

The density of air, ρ = 1.2 kg/m³

The power obtained from the windmill, 'P', is given as follows;

Where;

= 1.0 kg/(N·s²)

A = Cross-sectional rea of the the windmill =  π·D²/4 = π×(30 m)²/4 = 706.858347 m²

Plugging in the values, we get;

The power generated by the windmill, P ≈ 1363668.19438 W ≈ 1.364 MW.