## Time derivatives

1. The problem statement, all variables and given/known data

My question is how do I take the time derivative of (theta dot)^2?

2. Relevant equations

3. The attempt at a solution

Is the answer just 2(theta double dot)^1 or do you use chain rule 2(theta dot)*(theta double dot)?

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 Well, assuming theta is a function of time, you must use the chain rule!
 Recognitions: Gold Member Science Advisor Staff Emeritus I take that your "dot" refers to differentiation with respect to time, t,- I will use a prime since it is simpler here- and you are asking about the derivative of $(\theta')^2$. The derivative of any $(f(t))^2$ with respect to t is $2f(t)f'(t)$, by the chain rule, so the derivative of $(\theta(t)')^2$ is $2(\theta')(\theta'')$.