Finding string tension when a mass swings in a vertical circle

[PhysicsGirl]

Homework Statement

A mass of 100 g is tied to the end of an 80.0 cm string and swings in a vertical circle about a fixed center under the influence of gravity. The speed of the mass at the top of the swing is 4.00 m/s. What is the tension in the string when the mass is at the bottom of its swing?

Homework Equations

The Attempt at a Solution

I really don't even know where to start! Please help.

 

[belliott4488]

HINT: Don't worry about solving for speed as a function of angle or height, etc. (although you could). Think energy! What is it at the top? What must it be at the bottom? Now you can ask how fast it's going and what is the tension.