1. The problem statement, all variables and given/known data Water with mass density ρ are being shoot from a jet with cross sectional area A and velocity v0 at a man with mass m0. 1. Find the force acting on a man at rest (assume all the water are absorbed in the clothes) 2. Find the force acting on a man escaping at velocity v<v0. 2. Relevant equations dp/dt=ƩF 3. The attempt at a solution I calculated the momentum of a small water element dm = dmv0. this is the same as the momentum of the water and the man after the water hits him(no external forces): dmv0=(m0+dm)v v=(dmv0)/(m0+dm) The momentum of the man only after the water hit him is: dp=m0dmv0/(m0+dm). dp/dt=m0*(dm/dt)*v0/(mo+dm)=ƩF But i couldnt get an expression of the force without dm or dt. Thanks for the helpers!