# Calculating 'Push' Force to Maintain Constant Speed

## Homework Statement

A conducting rail in contact with conducting wires, oriented perpendicular to both wires, is pushed with constant speed, causing an induced current of 0.69 A. B = 0.50 T and R (Resistor) = 2.0

Calculate the "push" force necessary to maintain the rail's constant speed.

## Homework Equations

I assume I use F = q * v * b

## The Attempt at a Solution

I don't think I am using the correct equation here because there is no charge on the conducting rail. I am thinking I need to use an equation that I am not yet familiar with. I went to the chapter in my book over induction and I can't find any equations dealing with a 'push' force.

Doc Al
Mentor
You want the magnetic force on a current-carrying wire in a magnetic field, not the force on a single charge. Read this: http://hyperphysics.phy-astr.gsu.edu/Hbase/magnetic/forwir2.html" [Broken]

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Ohhh! Duhh. Lol. Thanks so much! That helped.

So, F = (0.69A)(0.34m)(.50T) = .117 N

And this would be considered the "push" force? Or would it be negative since the force is acting in the opposite direction?

Doc Al
Mentor
And this would be considered the "push" force? Or would it be negative since the force is acting in the opposite direction?
I assume they just want the magnitude of the force.

The induced current leads to a magnetic force on the wire. If you don't push the wire with a force opposite to the magnetic force to cancel it out, the wire will slow down due to the magnetic force. (This is the point of Lenz's law: The induced current is not "free"--you must push on the wire to maintain it.)

Thank you! That makes sense.