1. The problem statement, all variables and given/known data A toy rocket consists of a plastic bottle which is partially filled with water. The space above the water contains compressed air. At one instant during the flight of the rocket, water of density p is forced through the nozzle of radius r at speed v relative to the nozzle. Determine, in terms of p, r and v, the mass of water ejected per unit time from the nozzle 2. Relevant equations 3. The attempt at a solution I know the answer is πr2pv. But I am not sure of exact explanation why this is the case.