That's what 'I' got, whether or not it is correct is what I was asking? should it be a plus instead of a minus?
as in, I used implicit differentiation to turn 1/r into -1/r^2 * dr/dt. since in this case dr/dt = -V that gives V/r^2 etc etc
I'm a bit stuck on this question (which is homework so hints are more welcome than outright answers). The question is:
A very long wire carrying a current I is moving with speed v towards a small circular wire loop of radius r. The long wire is in the plane of the loop and is too long to be...