The Chain Rule: Videos & Practice Problems

A bungee cord stretches and compresses as a person of mass $m$ bounces up and down. The position $y$ of the person at time $t$ is described by:
$y\left(t\right)=A\cos \left(t\sqrt{\frac{k}{m}}\right)$,
where $A$ is the amplitude of oscillation, $k>0$ is the stiffness of the bungee cord, and $y\left(t\right)$ is positive when the person is above the equilibrium position. If the stiffness of the bungee cord is increased ninefold ($k\to 9k$), how will this affect the velocity of the person during oscillation?