There is an evil scientist who does not like people to show up unannounced to his lab. He made a trap room that will squeeze these guest using a hydraulic piston to move one of the walls. His last visitor was able to stop the wall from squeezing him. The evil scientist rigged a circuit so that when the wall is moving, an LED bulb will light to notify him. The circuit has a total resistance of 50 ohms and the bulb can carry no more than 20 mA. The room is 3 m high.