How to link two objects by rope

Hello everybody.

I have a problem. In my scene, i have an object that move along the curve (at present, curve is located under plane). This cube have reference on other object (for example car, not child). Our needs, that car move on the plane for a cube(nearly). Also, we needs, that gravity, and other physics influences on the car. This situation looks as a child pulls toy car, tied to a rope.
Can i use joint or other technology?
How i can connect these objects, using joint, for such behavior of machines.

At present, i try to use for towing two method:
1) steering behaviour, in this method cube is target, but speed of car and speed of the cube not equal. Increase distance between cube and car.
2) i was used joint. In this method connect is strong, and car flying to the cube.