Work and gravitational potental energy

[Shatzkinator]

Homework Statement

A thin rod, of length L = 2.00 m and negligible mass, that can pivot about one end to rotate in a vertical circle. A ball of mass m = 5.00 kg is attached to the other end. The rod is pulled aside to angle theta = 30 and released with initial velocity v= 0. As the ball descends to its lowest point, (a) how much work does the gravitational force do on it and b) what is the change in the gravitational potental energy of the ball - Earth system?.. etc.

Homework Equations

The Attempt at a Solution

In the solution, they show W = 5 x 9.8 x 2(1- cos30)

where do they get the 1-cos30??

 

[rootX]

W = Work at one step- Work at another step

= 5 x 9.8 x 2(1) - 5 x 9.8 x 2(cos30)