On my website you'll find similar problems with animations
Got to Calculus Animations
On the optimization and related rates page see walking towards the light and walking away from the light
A lamp is placed on the ground 100ft away from a wall. a max 6ft tall is walking at a speed of 10ft/sec from the lamp to the nearest point on the wall. When he is midway between the lamp and the wall , the rate of change in the length of his shadow is (in ft/sec)?