Unity3D Bullet Code

using UnityEngine;
using System.Collections;

public class Bullet : MonoBehaviour 
{
	public float Damage = 10;
	public float Speed = 1500;
	public PlayerController Player;
	
	void Start()
	{
                // Bullet Drop like in bfbc2
		rigidbody.AddRelativeForce(new Vector3(0,0,Speed), ForceMode.Impulse);
		Destroy(gameObject, 5f);
	}
	void OnCollisionEnter(Collision col)
	{
		col.gameObject.SendMessageUpwards("RecieveDamage", Damage, SendMessageOptions.DontRequireReceiver);
		Destroy(gameObject);
	}
}