How to find speed with Faraday's law

[Jacobs]

Homework Statement

A metal rod can slide on a rail without any friction in the presence of uniform magnetic field of B=1T which is perpendicular to the plane of the paper.The distance between the tracks is d=0.1m and the resistance given is R=0.1 ohm.The resistance of the rail is negligible and the mass of the rod is m=20g. A)How much force must be on the road exerted in order to move it with a constant speed of v=10m/s? B)The rod has been moved for t=2s and then it is released.How much work is dissioated on the resistor till the rop will stop?

Homework Equations

F=IBl=B^2*l^2*v/R

The Attempt at a Solution

According to first formula F=1 but for B i have no idea

 

[berkeman]

Welcome to the PF.

Could you please post the figure that goes with this question? It sounds like a classic sliding rail changing the total B*dA, but it's hard for me to be sure from the text of your post. Thanks.

 

[Jacobs]

1st one

 

[scottdave]

You might start here. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

The rails and the rod and resistor make an electric loop. You can find the area of that loop if you know the length, but for this problem, you are interested in the Change in the area when the rod moves. Since Phi = B*A, phi can change if B changes or (in your case) when A changes. It doesn't do a whole lot of good to have some formulas, unless you have an idea of where they come from. Then you'll understand which ones to use.

 

[scottdave]

This one talks about the force, which is what you're looking at. These are the concepts to consider, not how to solve the problem (yet). http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html

I hope this helps you get started

 

[Jacobs]

so formula is BdeltaA/delta(t) but still have no idea about how find find change in the area

 

[Jacobs]

Answer of B is 2?

 

[berkeman]

so formula is BdeltaA/delta(t) but still have no idea about how find find change in the area

The motion of the movable rod changes the area.

Answer of B is 2?

Please always show your detailed work so we can check it. Thank you.