A ladder 17 feet long is standing straight up against the side of a house. The base of the ladder is pulled away from the side of the house at a rate of 2 feet per second and the top of the ladder is moving down the wall of the house. How fast is the top of the ladder moving after 4 seconds? Solution length of rod remains constant let x be distance from origin , and y above the floor x*X + y*Y = 17*17 pythagoras theorem take derivative wrt t : 2x dx/dt + 2y dy/dt = 0 2x(2) + 2y dy/dt = 0 there should be some more information as value of either x or value of y then only possible.