1. The problem statement, all variables and given/known data During a rescue operation, a 5200-kg helicopter hovers above a fixed point. The helicopter blades send air downward with a speed of 70m/s . What mass of air must pass through the blades every second to produce enough thrust for the helicopter to hover? 2. Relevant equations ΣF = 0 3. The attempt at a solution Since the helicopter is hovering, the magnitude of the downward forces have to be the same as the upward forces. The only downward force on the helicopter is the weight = mg. So this must equal the upward forces. I can't figure out what the upward force is. I tried using impulse and momentum to find force, but the change in momentum is zero, so impulse is zero so that doesn't help me find the force of the air on the helicopter. I know that the force the blades exert on the air, the air exerts on the helicopter, and all I have is the velocity of the air from the blades.