Force of an electromagnet question

[radaballer]

Homework Statement

A solenoid which is 0 meters away from a ferrous piece of metal exerts how much force on it? there is 0.42 amps, and 1000 turns in the coil. the cross-sectional area is 2.8502e-4 meters^2

Homework Equations

Force = ((N x I)^2 x k x A) / (2 x g^2)

N = the number of turns in the solenoid
I = the current, in amperes (A), running through the solenoid
A = the cross-sectional area, in meters-squared, of the solenoidal magnet
g = the distance, in meters, between the magnet and the piece of metal
k = 4 x pi x 10^-7

The Attempt at a Solution

I am not sure how to attempt seeing that the 0 meters of separation would cause the force to be infinite according to the equation

 

[Simon Bridge]

Make sure you understand the equation and how it is applied.
Where did you get that equation - what is that part of your notes talking about?

 

[rude man]

Hint: magnetic pressure = energy density.

You also need to know the length of the solenoid. And finally you either have to know the length of the metallic object, or assume it is very long.