# Momentum Changes in a variable mass system.

1. Jun 2, 2004

### Faustian

Pleeeease help me. I have to do a twenty minute presentation on momentum changes in variable mass systems. I have everything done but examples. The equation I have is m(t)a=Rv where R is the rate the mass of the rocket is decreasing and v is the velocity of the gas ejected with respect to the rocket. Does anyone have any examples from the internet I can use? At least any realistic variables? I have absolutely NO idea what realistic numbers would be for this situation. Actually, to be honest, I'm not really sure how to use the equation. What would I have to have to solve for a sample? The velocity of the particles ejected, the time and rate of change of the mass? Then I would just use the rate of change and the time to find m(t) and I would solve for a? This is actually for AP Calculus, but I'm pretty sure this concept is a bit advanced for the highschool level (My physics teacher couldn't even help me, which is kind of sad). Please, any help will really be appreciated.

2. Jun 2, 2004

### Hypericum

Umm… ok. Well, that certainly sounds like an interesting presentation but a lot of work. I hope you're enjoying it.
There is a site by Michael Richmond, Dept. of Physics Rochester Institute of Technology, which should be helpful.
http://spiff.rit.edu/classes/phys311_t/workshops/w10a/rockets/rockets.html [Broken]
It lists two rockets and the fuel used in there deployment. You might have already considered this, but using cars as examples might be simpler, as you don’t have to consider changes in gravity and air density.

Last edited by a moderator: May 1, 2017
3. Jun 2, 2004

### Faustian

Thank you. That looks like it'll help. The thing is, most of the people in my calculus class haven't even taken a basic physics class. Because of this, I can make my problems as simple as possible. The samples I use won't even have ANY gravity or air resistance.