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P: 22
ah k. i followed the link to specific impulse and it helped me understand.

http://en.wikipedia.org/wiki/Specific_impulse
 Specific impulse (usually abbreviated Isp) is a way to describe the efficiency of rocket and jet engines. It represents the force with respect to the amount of propellant used per unit time.[1] If the "amount" of propellant is given in terms of mass (such as in kilograms), then specific impulse has units of velocity. If it is given in terms of weight (such as in kiloponds), then specific impulse has units of time. The conversion constant between the two versions of specific impulse is g.[2] The higher the specific impulse, the lower the propellant flow rate required for a given thrust, and in the case of a rocket the less propellant is needed for a given delta-v per the Tsiolkovsky rocket equation.
and it says the effective exhaust velocity is also the thrust divided by the rate of the flow of mass from the rocket. that makes sense. (and yeah, this is with the specific impulse being constant).