Hi, I've got a related rates problem I can't solve:

There is a dog and a cat. Initially the cat is located at (0,0) and the dog at (0, -a). The cat is moving along the x axis in the positive direction with a constant speed c. The dog is moving with a constant speed h, but its direction is always directly towards the cat. Identify the function y = f(x) that describes the trajectory of the dog.