A child is flying a kite. If the kite is 135 feet above the child's hand level and the wind is blowing it on a horizontal course at 7 feet per second, the child is paying out cord at ______ feet per second when 285 feet of cord are out. Assume that the cord remains straight from hand to kite.

Answer 1

I assume you have drawn a diagram of the situation. The length z of cord when the kite has flown to a horizontal distance x is

z^2 = x^2 + 135^2
so,
z dz/dt = x dx/dt

Find x when z=285, and you can find dz/dt.