How much air must be pushed downward at 40.0 m/s to keep an 800-kg helicopter aloft?
A) 20 kg/s
B) 196 kg/s
C) 32 000 kg/s
D) 201 kg/s
E) 186 kg/s

Question

How much air must be pushed downward at 40.0 m/s to keep an 800-kg helicopter aloft?
A) 20 kg/s
B) 196 kg/s
C) 32 000 kg/s
D) 201 kg/s
E) ​186 kg/s

Quizplus · Accepted Answer

The lift force on the helicopter is equal to its weight, which is 800 kg * 9.8 m/s^2 = 7840 N. The air must be pushed downward at a speed of 40.0 m/s to create this lift force. The mass flow rate of the air is therefore 7840 N / (40.0 m/s) = 196 kg/s.

How Much Air Must Be Pushed Downward at 40