FireballMove.cs

using UnityEngine;
using System.Collections;

public class FireballMove : MonoBehaviour {
	public float speed;
	private Rigidbody2D fireRB;
	public Vector2 move;

	// Use this for initialization
	void Start () {
		fireRB = GetComponent<Rigidbody2D> ();
		fireRB.velocity = (move * speed);

	}

	// Update is called once per frame
	void Update () {
		//fireRB.MovePosition((Vector2)transform.position + move*speed);
	}

	void OnCollisionEnter2D(Collision2D c){

		Destroy (this.gameObject);
	}
}