Puzzler

Sam was getting to be an old hand with VisSim, but ran into a problem modeling the electric steering mechanism in his solar powered car. He had carefully modeled the motor force, the frictional resistance of the wheels and linkage, integrated force over mass to get velocity and integrated velocity to get position. He even included a limit block after his velocity integral to limit the range of motion. What he noticed was that when he hit the stops and then reversed direction on velocity, there was some significant lag time before seeing any motion off the stops. The longer he drove into the stops, the longer it took when he reversed motor steering direction before he saw any actual motion. Specifically, why does the linkage not move when velocity goes negative at time 2? What was Sam's problem?

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