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Re: Can a system's mass vary?



Not if you are careful to properly identify v as the relative velocity
of the car and the grain elevator.

Mark

Dr. Mark H. Shapiro
Professor of Physics, Emeritus
California State University, Fullerton
Phone: 714 278-3884
FAX: 714 278-5810
email: mshapiro@fullerton.edu
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-----Original Message-----
From: Robert Cohen [mailto:Robert.Cohen@PO-BOX.ESU.EDU]
Sent: Sunday, November 09, 2003 9:56 AM
To: PHYS-L@lists.nau.edu
Subject: Re: Can a system's mass vary?

On Sunday, November 09, 2003 12:27 PM, Mark Shapiro wrote:

But, what about more mundane problems where it seems to me=20
that it is much easier to consider the mass of the system to=20
be varying. Exampl=3D es include conveyor belts and=20
escalators, and the simple problem of keep=3D ing a hopper car=20
moving at constant velocity while it is moving under a grain=20
elevator that is dumping grain into it. F=3D3Ddp/dt works for=20
th=3D ose problems when you allow the mass vary.

Does it matter what the speed of your inertial reference frame
is? In other words, does it still work if you observe the
grain elevator/hopper car system from a moving train?>

____________________________________________________
Robert Cohen; 570-422-3428; www.esu.edu/~bbq
East Stroudsburg University; E. Stroudsburg, PA 18301