Answer to Question #81570 in Physics for sal

Question

Imagine a flying super-dog that is able to accelerate horizontally and vertically. You are going to play fetch with this flying dog. Imagine throwing a rock up and forwards so that it follows the usual parabolic path away from you. As you throw the rock, the dog is waiting a few meters behind you. What is the acceleration vector for the dog if it flies in a straight line to catch the rock just as it passes the highest point on the parabola?