The double$-$excited electromechanical system shown in the given figure moves horizontally. Assume that resistance, magnetic leakage, and fringing are negligible; the permeability of the core is very large; and the cross$-$section of the structure is $\backslash (\backslash$mathrm$\{$w$\}\backslash$times $\backslash$mathrm$\{$w$\}\backslash ).$

NOTE: This is a multi$-$part question. Once an answer is submitted, you will be unable to return to this part.

Problem $14\mathrm{.}035.$c $-$ The magnetic force on the movable part as a function of its position

Identify the force on the movable part as a function of its position.

multiple choice.