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.