Finding Force Given Angle: A Last-Minute Attempt

[iiiiaann]

Homework Statement

Homework Equations

this is what i think i figured out to be the equation for force as a function of θ:

F(θ) = (μmg)/(cos(θ) + μsin(θ))

The Attempt at a Solution

I tried to find extrema using the numbers given to figure out the angle, but the number i am getting is not right. This is kind of a last ditch effort as I need to finish this within a half hour

 

[Delphi51]

You aren't asked to find an angle. Don't use any formula with an angle in it! For the magnitude, start out with "magnetic force = friction force" and fill in details until you can solve it for B.
For the direction, apply your hand rule to the lower diagram. The answer will be up or down (which you must translate into y or -y) because it must be perpendicular to both the current and the slide.