What Is the Maximum Vertical Acceleration of a Pendulum?

[Luke1121]

Homework Statement

A pendulum has a length of 0.5m and an amplitude of oscillation of 8 degrees, what is maximum vertical acceleration

Homework Equations

$X=Acos(\omega t + \phi)$
$\omega =\frac{2\pi}{T}$
$T=2\pi \sqrt{\frac{l}{g}}$

The Attempt at a Solution

Taking the second derivative with respect to time for
$X=Acos(\omega t + \phi)$ then
$a=-\omega^2Acos(\omega t + \phi)$
$\omega$ can be obtained using $T=2\pi \sqrt{\frac{l}{g}}$ and doing $2\pi$ divided by this, but I am unsure how to find $A$ Am I on the right lines? Thanks

 

[nasu]

What is A in this formula?
Remember that you need vertical component of acceleration.