# Homework Help: Terminal Velocity of magnet down a copper tube

1. Mar 30, 2016

### krisal

1. The problem statement, all variables and given/known dataI
I am trying to find an equation that relates the velocity of 3 magnet when it falls down a copper tube to my measurement.

The length of the copper tube is L=0.24m,
The total mass of the 3 magnet is m = 4.98x10-3kg
magnetic flux density B = 428mT,
the thickness of the tube w = 0.05cm
inner radius is r= 0.7cm,
the resistivity of the copper tube is p = 1.68x10-8 ohmm
resistance of copper tube is R= 1.77x10-4 ohms
and the terminal velocity that I measured is v = 0.104m/s

2. Relevant equations
I obtained this equation e=(B^2L^2v)/R from this procedure

e =Blv=IR
F = BIL rearranging for I = F/BL and sub to equation above
e=(B^2L^2v)/R

also

I found an equation in the internet that F = C(Bwv)/p which C is the constant of proportionality but it did not tell what C is.

3. The attempt at a solution

I used the first equation but the answer for v is much smaller v = 8.2x10-4m/s
I would use the second equation but I do not know what C is

I want an equation that is not very complex to derive

Last edited by a moderator: Mar 30, 2016
2. Mar 31, 2016

### Staff: Mentor

Did you check the units of your answer? And where exactly does a speed occur there?
Not all problems have easy answers.

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