A rescue helicopter of mass 810 kg, supports itself in a stationary position by imparting a downward velocity, v, to the air in a circle of radius 4.0 m. The density of the air is 1.20 kg m-3. Calculate: (i) the value of v (ii) the power, P, required to support the helicopter So, I do have the solution to part one, which is 11.5 ms-1. However, the solution for ii eludes me. The answer sheet does something weird: Power = 0.5(pi*4^2)(1.2)v^3. From the first term I'm guessing they're using E=.5mv^2, but why is the velocity raised to the third?