What is the equation for U in the Equipartition Theorem?

[Hypervalent_Iodine]

Homework Statement

Use the equipartition theorem to estimate the heat capacity of
(i) carbon dioxide, (ii) methane.

Relevant Equations

C=dU/dT

.

 

[DrClaude]

Per PhysicsForums rules, we require that you present an attempt at a solution.

In your relevant equations, an equation for $U$ would also be useful.