In order to safely land a lunar module, it must have a speed near 0 m/s as it touches down on the moon's surface. The module must fire its thrusters as it descends, counteracting the downward acceleration due to gravity and thus reducing its speed as it nears the surface.
In this simulation, the thrust is given by the product of the exhaust velocity (the speed at which combustion gases exit the propelling nozzle) and the rate of fuel consumption. If either of these rates is 0, the net thrust will also be 0 and the module's downward acceleration due to gravity will be unimpeded.
The mass of the module in this simulation is based upon the averages for NASA's Apollo Lunar Modules. Its total mass is 10334 kg, with 8200 kg accounting for the fuel and the remaining 2134 kg accounting for the module itself.