The diagram shows a wind turbine.

(a) The blades of the turbine are 20 metres long. On average, 15 000 kg of air, moving at a speed of 12 m/s, hit the blades every second.

Using an appropriate equation, calculate the kinetic energy of the air hitting the blades
every second.

Show clearly how you work out your answer.

Kinetic energy = ......................... J
(2 marks)

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(b) Part of the kinetic energy of the wind is transformed into electrical energy.

The diagram shows that, for the same wind speed, the power output of a turbine, in kilowatts, depends on the length of the turbine blades.

Give a reason why doubling the diameter of the blades more than doubles the power output of a turbine.

(1 mark)

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From Q4 P2 AQA January 2011 (Higher)