Props physic

Hello, could somebody help me with one think, I mean props. Games like watch dogs, gta, traffic lights, road sings can not fall until they will be hit by heavy object. When car will hit those objects, object change from kinematic to nonkinematic and car continues his route. I tried do somethink like this in unity.
Pseudo code:

Oncollisionenter(collision)
if(relativevelocity.magnitude/mass>minforcetofall)
{
vector3 vel = collision rigidbody velocity;
gameObject iskinemtic=false;
collision rigidbody velocity=vel;
}

And it works but physic is faster than oncollisionenter and physic stops my vehicle before vehicle will get velocity from vel. So there is somethink like vehicle lag. How can I make it smoothe, without stop car?
Car must stop if will hit object with low speed (like hitting wall) but with highspeed car can not stop and prop have to fall.

Don’t set the rigidbody to kinematic. Instead do this:

void Start(){
     rigidbody.useGravity = false;
     rigidbody.Sleep();
}

void OnCollisionEnter(Collision collision){
     rigidbody.useGravity = true;
}

What this will do is “freeze” the rigidbody in Start(), and when it collides with something, useGravity is enabled and the rigidbody will interact normally with physics.

Or maybe there is something like wake up rigidbody after specified force?