Since has a mass and only mass M3 Playing on a see-saw (of negligible mass) was pretty boring.
In the above diagram, Dr. L. is on the very left end of the see saw, with Kepler directly over the middle of plank (total length L). The rocket is attached to the very right end of the see-saw and firing (Thrust T = 8Mg) at an angle of 0 above the horizontal as shown. The system is in static equilibrium.
Where is the fulcrum located relative to the left end (shown as x in the diagram)? Your answer should be in terms of L only.