Can energy double?

[Bentoptics]

Sorry everyone I seemed to have dropped the ball here (no pun intended)
I need to go over that last set of equations and see where I messed up.
Attached are the corrected results.

@Zhang Yalin
I do not see any extra energy from this system. There is inertia to overcome in the car when the weight is first released.
BentOptics

[Zhang Yalin]

You should not add the weight of the ball and the car together. It's not right to do so.
If the power of the car comes from the other sources, how to add it ?

[Bentoptics]

The car is moving when the weight falls due to the tension of the string attached to it.
If there were added forces on the car you would be able to see it.
Such as the string would go limp if the car is able to accelerate from added forces.
The reverse would be true as the string could break if the forces were suddenly forcing the car backwards.
You could make this system and when you release the weight try doing this at the same time drop another weight all by itself no strings attached and I would bet the free weight would hit 10m when the one on the string is only at 5m. Can you show a video of this system perhaps I am looking at it incorrectly.

BentOptics

[Zhang Yalin]

If only you would contrast the ball with the car and the free ball 's dropping, then you will get it.

[Bentoptics]

Zhang Yalin
I do not think I will get it.  I guess I can not see outside the proverbial box.

BentOptics