I'm having trouble understanding motion with non-constant mass.(adsbygoogle = window.adsbygoogle || []).push({});

Specifically, if (dm/dt) is positive when the mass of the system is increased, I find that:

[tex]\vec{F} = \frac{dm}{dt}\vec{u} + \frac{d\vec{v}}{dt} m [/tex]

Where u is the velocity of the mass leaving/entering the system relative to the system and dm/dt is the rate of change in the mass of the system.

If I set F = 0, in a situation where there are no external forces, I get:

[tex]\frac{d\vec{v}}{dt}m = -\frac{dm}{dt}\vec{u}[/tex]

But if dm/dt is negative, doesn't this mean the acceleration due to mass leaving the system dv/dt is in the same direction as u, the velocity at which the mass is leaving the system?

Edit: Sorry for posting this in the wrong forum. I saw the warning, but I assumed it meant not posting specific homework questions, rather than general queries.

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# Motion with non-constant mass

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