Physics not applying to the animated object after the animation ends ?!

Hi guys,

I'm trying to animate an objects rotation from 0 degree to -80 degree going up like a cap and then turning back to its original rotation which was 0 degree. The reason I want to animate it is because when I code this in c# script "Time.deltaTime" doesn't work on negative values and the rotation is done directly without being updated as it should update with Time.deltaTime and I don't wan't to make it this way. So, I have done the animation of this object now and it rotates from 0 to -80 degree (from the rest position going upward), but the physics of the object don't apply anymore. I mean the object goes to upward position ( -80 degree) but doesn't fall down to its rest position ( 0 degree), meaning that the physics don't apply anymore to the object and I don't know why does this happen.

I forgot to say that the object has a rigidbody with gravity checked on, a hinge joint connected with another object below which is kinematic and has a collider to stop the object above at 0 degree( rest position). The animation works well. It starts playing from 0 to -80 degree and it stops there. All I want is to make the object fall down to its start position (0 degree). In Animator I have unchecked Apply Root Motion.

Hope someone knows where the problem is cause I have been searching all the day about this and didn't fix anything. Thanks in advance. Sorry for my english and the long description of the problem. :D ;)