Inserting Dielectric and Direction of Force on It

[The Head]

Homework Statement

A slab of width d and dielectric constant K is inserted a distance x into square parallel capacitor
plates of side L. Determine the magnitude and direction of the force on the slab (Assume V₀ is constant.

Homework Equations

F= d/dx(U)
U=1/2CV²

The Attempt at a Solution

I am through determining the magnitude of the force (V₀²*ε₀*(K-1)/2d, but am confused as to why the direction of this force is toward the left, which is what my book, Giancoli, says. I have attached a picture with this post.

The way I rationalized it was that because the dielectric raises the capacitance and the potential difference is held constant, the stored energy, U, should be higher with the dielectric, and thus you add energy to the system by putting in the slab. Thus, I would think that the electric field would be trying to push the slab out (to the right) to attain a lower energy state. What am I missing?

 

[BigJDubs]

I understand the force is trying to minimize energy, but why would it be pushing the slab to the left? Thanks for any help.