## Max Velocity of a Water Rocket

Find the maximum velocity of a PET bottle rocket on a day with temperature 30 degrees celcius and pressure 1 atmosphere, if the pressure inside the bottle was 40 psi and the volume of water in the bottle was 300 mL.

I know of Tsiolkovsky's equation but i'm not quite sure how to use it here. Any help appreciated

EDIT: Pretty sure I need to find the exhaust velocity of the water given the above details. I have a formula that says $$\Delta p = \frac{1}{2} \rho v^2$$ where $$\rho$$ is the density of water and p is pressure that (I think) gives the exhaust velocity v but I don't know where the formula came from or if it is even correct.

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 Feel free to ignore the first part of the question. I just need someone to explain that relationship between pressure and exhaust velocity there. Also I'm guessing that the density of water changes with temperature?