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

A small sphere with mass m is attached to a massless rod of length L that is pivoted at the top, forming a simple pendulum. The pendulum is pulled to one side so that the rod is at an angle θ from the vertical, and released from rest.

When the pendulum rod is vertical, what is the linear speed of the sphere? Express your answer in terms of g, θ, L.

**2. Relevant equations**

[itex] a = \frac{v^2}{r}[/itex]

**3. The attempt at a solution**

I’m not sure how to derive acceleration at this point. I know that

[itex] mg-T=ma [/itex]

and that you could insert the acceleration derived here for the centripetal acceleration equation to derive velocity

But otherwise I’m kind of lost

[itex] \sqrt(aL) = v [/itex]

http://ift.tt/1nSWaDE