# Water Rocket - Rate at which water exits

by NMS09
Tags: exits, rate, rocket, water
 Sci Advisor HW Helper P: 6,653 The force depends on the speed of the water being ejected. Assume that the water comes out at a speed v relative to the container. The rocket thrust is, as you have stated: $$F = \Delta p/\Delta t = v\Delta m/\Delta t$$ where $\Delta m$ is the mass of a volume of water ejected in time $\Delta t$. Since the water is being ejected at the speed v, $\Delta m$ is $\rho \dV = \rho A\Delta s = \rho Av\Delta t$. So the rate of mass expulsion is $\Delta m/\Delta t = \rho Av$ Work out the expression for force and then find the speed that is needed to reach 300 N. From that you can calculate the rate at which mass has to be ejected. AM