a bungee-jump cord has length $\ell$ and is initially folded back on itself, as shown in the figure. the jumper has mass $m$. after she jumps (or rather falls) off the platform, she is in freefall for a height $\ell$. after that, the spring becomes stretched. assume that it acts like an ideal spring with a particular spring constant. (this applies only during the stretching motion, of course; the cord can't support compression like a normal spring.) it is observed that the lowest point the jumper reaches is a distance of $2\ell$ below the platform. what is the jumper's maximum speed?