How to move ball as fast as it pulled back for 2D game in Unity 4.3

Hi, I am working on 2D game development in Unity 4.3. I am making Ball Popper type game, so user pulled back the ball and when he/she release it, it goes to as fast as it pulled back. So I want to get experienced developer suggestion here, how can I write smart code to accomplish this task. I also attached following code with this post. Kindly look into this and suggest me better approach.

 if(Input.GetTouch(0).phase == TouchPhase.Began) {
             RaycastHit hit;
             Vector3 v3;
             Ray ray  = Camera.main.ScreenPointToRay(Input.GetTouch(0).position); 
             if(Physics.Raycast(ray,out hit) && (hit.collider.tag == "Drag"))
             {
                 Debug.Log("Object hit with Dragable child object...");
                 dragging = true;
             }
         }
         if(Input.touchCount>0 && Input.GetTouch(0).phase == TouchPhase.Moved && dragging) 
         {
             Debug.Log("Move object.........");
             collider2D.sharedMaterial.bounciness = 0.9f;
             collider2D.enabled = false;
             collider2D.enabled = true;
             Vector2 touchdeltaposition = Input.GetTouch(0).deltaPosition;
             anglex = (float) (touchdeltaposition.x * Time.deltaTime*speed);
             angley = (float) (touchdeltaposition.y * Time.deltaTime*speed);
         
             elevationAngle = new Vector3(anglex,angley,0); 
             Vector3 elevation = Quaternion.Euler(elevationAngle)*transform.forward;
             rigidbody2D.AddForce(elevation);
             rigidbody2D.velocity= new Vector2(anglex,angley);
         }
         if(Input.GetTouch(0).phase == TouchPhase.Ended){
             dragging = false;
         }

This code move ball when user swipe onto ball, but I just want to do this when user pulled back this ball. Thanks in advance...