InterviewSolution
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InterviewSolution
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The helicopter has a mass `m` and maintains its height by imparting a downward momentum to a column of air defined by the slipstream boundary as shown in figure. The propeller blades can project a downward air speed `v_0`, where the pressure in the stream below the blades is atmospheric and the radius of the circular cross section of the slipstream is `r`. Neglect any rotational energy of the air, the temperature rise due to air friction and any change in air density `rho`. If the power is doubled, the acceleration of the helicopter is :- A. `(mg)/(2r) sqrt(mg)/(pi rho)`B. `(mg)/(r ) sqrt(mg)/(pi rho)`C. `(2 mg)/(r ) sqrt(mg)/(pi rho)`D. `(mg)/(r ) sqrt(mg)/(2pi rho)` |
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Answer» Correct Answer - A Thrust `= F = rhoAv^(2) " " [A = pir^(2)]` at equilibrium `rhoAv^(2) = mg` Power `P = Fv = rhoAv^(3)` `= (mg)/(r ) sqrt((mg)/(p pi))` |
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