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July 22, 2014

July 22, 2014

Posted by **sonia** on Tuesday, October 7, 2008 at 10:40pm.

Model rocket engines are sized by thrust, thrust duration, and total impulse, among other characteristics. A size C5 model rocket engine has an average thrust of 5.26 N, a fuel mass of 12.7 g, and an initial mass of 25.5 g. The duration of its burn is 1.90 s.

If this engine is placed in a rocket body of mass 57.5 g, and if the rocket is fired in outer space, what is the final velocity of the rocket? Assume the fuel burns at a constant rate.

- physics -
**drwls**, Wednesday, October 8, 2008 at 2:24amYou need to derive or find the "rocket" formula for the velocity of an object that has a fixed force T applied while its mass is decreasing. Calculus is needed to derive it.

You can find it at

http://www.ebtx.com/mars/rocketeq.htm

You will need the rocket exhaust velocity, Ve.

You can get if from

T = dm/dt * Ve

where dm/dt is the rate of mass release, 12.7*10^-3 kg/1.90 s,

and T is the thrust in Newtons

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