How to get max velocity for simple pendulum

[PhizKid]

Homework Statement

A simple pendulum has a ball at the end of mass 5 kg and the length of the string is 5 m. Given $\theta = 0.0800 \cdot cos[4.43t + \phi]$ find the maximum velocity

Homework Equations

$\frac{1}{2}mv^2 = \frac{1}{2}kA^2$

The Attempt at a Solution

$\frac{1}{2}mv^2 = \frac{1}{2}kA^2 \\\\<br /> mv^2 = kA^2 \\\\<br /> v = \sqrt{\frac{kA^2}{m}} \\\\<br /> v = \omega \cdot A$

But the solution is $v = \omega \cdot Length \cdot A$. Why is it omega * the length * the amplitude?

EDIT: My friend helped me solve it:
w = dtheta / dt = -4.43*.08*sin(4.43t + phi)

w_max => 4.43t + phi = 3pi/2 => w_max = 4.43*.08

v_max = 4.43*.08*R = 5*4.43*.08

 

[Simon Bridge]

That's the one - it's what you get when you differentiate the displacement-time function: if you understand the displacement-time relationship you understand the velocity-time relationship.