What Angle Does the Plumb Bob Make with the Vertical on a Sliding Frame?

[Jstew]

Homework Statement

A plum bob suspended from a frame settles to a steady position as the frame slides down a frictionless inclined plane. What is the angle the plumb bob makes with the vertical during the slide?
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Homework Equations

The problem is from a section introducing Newton's Laws. I assume this problem is about inertia.

The Attempt at a Solution

Utterly no idea how to go about this, although I assume the answer is alpha=theta since that's the clean way the answer could come out.

 

[Jstew]

I figured it out. Set T to Fg and the T and m cancel out, leaving tan(theta)=tan(alpha)