Finding tension of a swinging mass

[hongus]

Homework Statement

A m = 5kg monkey swings on a vine the length l = 4m. His initial angle is theta = 25 degrees and he is moving at v = 2 m/s at the instant he begins his swing.
a. What is the tension in the string at the bottom?
b. What is the tension in the string at theta = 15 degrees?
Here's a picture of the diagram, not necessary but makes it easier

Homework Equations

I'm not really sure but here's a few.
k = (1/2)mv^2 + mgh
u = mgh

The Attempt at a Solution

I have no idea how to involve the theta into the equation, so I can't even really get started. Sorry for being so bad at physics :( If it helps, at the moment we're learning about the conservation of energy, in kinetic and potential energy. Thank you for reading.

 

[mishek]

Do You know the meaning of equations you wrote?

 

[voko]

Start with the free body diagram.