posted by Kyle on .
During a rescue operation, a 5600-kg helicopter hovers above a fixed point. The helicopter blades send air downward with a speed of 69 m/s. What mass of air must pass through the blades every second to produce enough thrust for the helicopter to hover?
Strictly speaking, you also need to know the vertical velocity component of the air entering the blades from above. It is not zero.
They probably want you to use
Weight = V * dm/dt,
and solve for dm/dt, the air mass flow through the blades, but this is a flawed problem.
I do not endorse their answer