Re: Newton's second law

[Advanced Physics Forums <admin@ADVANCEDPHYSICS.ORG>]

There is a rocket problem like that in chapter two of Marion I think...

You had to consider the rate of the change of mass of the rocket as fuel
burned.

I'd have to find my book though
----- Original Message -----
From: "SSHS KPHOX" <kphox@CHERRYCREEKSCHOOLS.ORG>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, November 06, 2003 2:02 PM
Subject: Re: Newton's second law


> Forum for Physics Educators <PHYS-L@lists.nau.edu> writes:
> > Newton' second law:
> >
> > F = dp/dt= mdv/dt + vdm/dt
> >
> > In the third term, what is v?
>
> My read would be that it is the velocity of the mass at some moment. F is
> a function of time. In most introductory work we ignore the dm/dt as = 0.
> Thus it does not matter what v is.
>
> I suspect this is a useful term in rockets and jet planes where thrust
> comes from mass being expelled at a specific velocity and at a specified
> rate.
>
> Ken Fox