Getting id of object

public GameObject hazard;
Rigidbody gm=Instantiate (hazard, spawnPosition, spawnRotation) as Rigidbody;
gm.AddForce(0f,50,0f);

I am trying to get id of created object and add force to it.
Above code is giving object reference not set to instance of object error.

How do i do this

 

With "as" you are trying to typecast your GameObject to a Rigidbody. But it's not a Rigidbody (even if it has a Rigidbody component). So the typecast will return null. I think you mean to do:

Code (CSharp):

1. GameObject noob = Instantiate(hazard, spawnPosition, spownRotation) as GameObject;
2. Rigidbody gm = noob.GetComponent<Rigidbody>();
3. gm.AddForce(0, 50, 0);

(Though adding a force for a single frame like this won't have a very good effect — you generally need to add force over several frames. For a newly spawned object, you're often better off simply setting the rigidbody velocity instead.)