Two Vehicle Model 
An example of a physics problem which requires the solution of
simultaneous equations, this problem has one vehicle start from rest as a
second vehicle passes it. The first vehicle is accelerating while the
second is traveling at constant velocity. At what point (time and
distance) will the two pass again?
After the velocity and acceleration models have been built, this is a natural extension, though students have to be led to the realization that there are now two objects and each requires its own set of stocks and flows. Once they picture that, they seem to be able to build the model.
Car_Distance(t) = Car_Distance(t  dt) + (Rate_of_change_of_Car_Distance)* dt INIT Car_Distance = 0 Rate_of_change_of_Car_Distance = Car_Velocity Car_Velocity(t) = Car_Velocity(t  dt) + (Rate_of_Change_of_Car_Velocity)* dt INIT Car_Velocity = 0 Rate_of_Change_of_Car_Velocity = Car_Acceleration Truck_Distance(t) = Truck_Distance(t  dt) + (Rate_of_change_of_Truck_Distance) INIT Truck_Distance = 0 Rate_of_change_of_Truck_Distance = 21 Car_Acceleration = 6 
