adding force to an instantiated gameobject in required direction

hi to all thanks for unity .i got struck up in a scenario where flight has to drop some objects on to the ground such that user will give the force direction (up/down/left/right)so that the object has to fall in that respective direction.i applied rigid body to the object that has to fall(cubefall) and i applied force aswell bt its seems to be having zero impact on the object by the force function.

         if(Input.GetKeyDown(KeyCode.O))
 
            {
 
             
 
              cubefall.rigidbody.useGravity = true;
 
             Instantiate(cubefall,InstantiatedPlane[tank.planenomisile].transform.position,cubefall.transform.rotation);
 
             
 
             
 
             
 
         }
 //for the object to project up(force which drives the object //in upward direction and then should fall down
         if(Input.GetKeyDown(KeyCode.UpArrow))
 
                {
 
             
 
             Instantiate(cubefall,InstantiatedPlane[Strela_Own_Tank.planenomisile].transform.position,cubefall.transform.rotation);
 
             cubefall.rigidbody. AddForce(transform.up* 300,ForceMode.Force );
 
             cubefall.rigidbody.useGravity = true;//as it has to fall down
 
             //cubefall.rigidbody.velocity = transform.TransformDirection(new Vector3(0,10,0));
 
             //cubefall.rigidbody.AddForce(transform.forward * 200);
 
     //i tried with all the statements that has been //commented 
 
 
 
             
 
             }

thanks in advance.code snippet is appreciated.