A ladder 10 meters long is leaning against a vertical wall
with its other end on the ground. The top end of the
ladder is sliding down the wall. When the top end is 6
meters from the ground is sliding at 2m/sec. How fast is
the bottom moving away from the wall at this instant?
Mathematically, the ladder problem is
almost identical to the circle
problem that we did earlier. The extra
feature is that it's a story problem. We have to draw a picture
and
think about the variables to see that $x^2 + y^2$ is a constant.