(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

We're currently studying Momentum & Collisions and Work and Energy

Use algebra – no Calculus

I’d appreciate help in setting it up. I seem to be missing one equation since I keep coming up with two unknown variables.

A water rocket (2-liter half filled with water and pressurized with compressed air) can develop a thrust of 300 N.

Question: At what rate would water have to come out of the rocket to develop that thrust?

The jet of water emerging from the bottle has a diameter of 2.2 cm. (.022 m.).

The water density is 1,000 kg/cu. m.

The answer provided is 10.7 kg/s.

2. Relevant equations

Equations we’ve been using recently:

Momentum: p = mv

Change of momentum: F = delta p / delta time

Force: F = ma

Force & Impulse: F = mvf - mvi / delta time

Conservation of Momentum: m1v1,i + m2v2,i = m1v1,f + m1v1,f + m2v2,f Note: Those are subscripts after v1 , ve, etc. I need to learn how to use the formulas on this site.

3. The attempt at a solution

I calculated:

The area of the exit hole = 1.52 x 10^-3 m^2

Water in the rocket = 1 kg

I then tried the convservaton of momentum equation but could not get the 300 N into a form to use on one side of the equation. Everything I tried seem to need a "delta t" value, which I don't know and was not given.

The free body diagram has the forward thrust of the rocket created by the rearward explusion of the presurized water. The 300 N must overcome earth's gravity (-9.81 m / sec^2).

Sorry for not being more organized, but I've spent 3 or 4 hours going around on this one.

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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# Water Rocket - Rate at which water exits

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