Homework Help: Give the magnitude of the magnetic field that will.

Give the magnitude of the magnetic field that will.......

1. The problem statement, all variables and given/known data



Suppose the rod in the figure has mass m = 0.38 kg and length 26 cm and the current through it is I = 40 A.

If the coefficient of static friction is u_s = 0.49, determine the minimum magnetic field B (not necessarily vertical) that will just cause the rod to slide. Give the magnitude of B.

Express your answer using two significant digits.

2. Relevant equations

F = IBd
F = u_sF_N

3. The attempt at a solution

Since its just "just beginning to move", I know that the two forces are equal to eachother.

So:

IBd = u_sF_N
IBd = u_smg

which means that:

B = (u_smg) / Id

I plug in the values (after converting them to standard SI units), and I get .175 T. To two significant figures would be .18. But thats not right, I also tried .17, not that either, .2 was also wrong. I don't know what I'm doing wrong.

 

Re: Give the magnitude of the magnetic field that will.......

never mind, i figured it out. Our teacher gave us a message saying that if you tilt the mag field west, it will reduce the normal force, and then the overall magnetic field strength. I modified the equations to make them functions of theta. Then from there, I found the value of theta that gives a minimum for B.