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.