Ok, I think I might have missed a key point in this class from a few weeks ago but anyways.(adsbygoogle = window.adsbygoogle || []).push({});

There is a truck of mass M, who has a constant force F applied to it. The truck is also being filled with coal at a constant rate b kg/s. I'm supposed to find an expression for the velocity of the truck.

First I tried:

F = ma

a = F/m

Then try to integrate both sides w.r.t time to get velocity, but since the mass depends on time as well, I get an expression involving ln(m).

So then I tried it this way:

F = dp/dt

Integrate both sides,

Ft = p = mv = (M+bt)v

v = Ft/(M+bt) which is the desired result.

I think I remember something from class about the Force more accurately being the change in momentum, and not necessarily the mass-acceleration product. Was this question just to emphasis that point? I think I'll have to go read the text

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# Homework Help: A truck with growing mass

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