Help! A physics question! I don't even know where to begin :(

Question

The idea that static magnetic fields might have a therapeutic vale has been around for centuries. A magnet disk is 3.0mm thick and has a field strength of 5.4 x10 ^-2 T at the center of the flat surface. The magnetic field strength points away from the center of the disk is inversely proportional to h^3, where h is the distance from the mid-plane of the disk. How far from the surface of the disk will the field strength be reduced to that of the Earth (5.0x10^-5 T)

Answer 1

Actually, I have this same question on my final exam and that isn't the way to calculate it because the strength is INVERSELY proportional, so:

B(h) = 5.4 x 10^-2 / h^3 gives the strength of the field,

and we want to know when B(h) = 5.0 x 10^-5, so set:

5.0 x 10^-5 = 5.4 x 10^-2 / h^3 , and solve for h.

This gives you an answer in meters (since that is the SI unit, and it is not otherwise specified), and the distance from the center, so subtract 3.0 mm (or 3 x10^-6 m) from your answer and that should be the distance form the surface.

I think this is right, and this is what I am using for my answer, I can't be sure though

Answer 2

The B field of the disk is

B(h) = (5.4 x10 ^-2 T ) h^3

At what value of h does this function have the value B(h) =5.0x10^-5 T ?

In other words find h when:

5.0x10^-5 = (5.4 x10 ^-2) h^3