The question is: A pump raises 1800 litres of water per minute through a vertical distance of 9m. Given that 1 litre of water has a mass of 1kg, find the power developed by the pump if the water is delivered at 12m/s. My thoughts are as follows. If the pump raises 1800kg of water per minute, then it must raise (1800/60)kg of water per second, which is 30kg per second. It's raising this against the force of gravity, so Force = ma = 30*g. Work done = force*distance = 30g*9 = 291g. Power is work done / time, but I've modelled it per second so power = 291g. Obviously that can't be right as the thing states it's delivered at 12m/s and I haven't used that. Please help.