Finding angle of cable when pendulum is at its highest point

[kurispice]

Homework Statement

Please see attached photo. It is problem 54.
My difficulty is that I am not sure if I marked out the correct forces in the work-force equation. Without the height, I can't find the angle. I was going to use the formula: Δx=radius (times) Δθ
However, I'm not even sure this is the right equation to use once I find the height. Should I use kinematic equations instead?

Homework Equations

Attached photo listing useful information for solving equation.

The Attempt at a Solution

Attached photo, written on notebook paper.

Thanks for your help!

 

[rock.freak667]

Draw a vertical line which and label it as the length of your pendulum string, and then draw the bob at the angle θ and then just draw a horizontal line through the bob when at the angle θ.

You can use simple trigs to obtain the angle.