private Vector3 touchPosition;
    private Rigidbody2D rb;
    private Vector3 direction;
    private float moveSpeed = 10f;

    static GameObject go;

    private void Start()
    {
        rb = GetComponent<Rigidbody2D>();
    }

    private void Update()
    {
        if (Input.touchCount > 0 && gameObject == go)
        {
            Touch touch = Input.GetTouch(0);
            touchPosition = Camera.main.ScreenToWorldPoint(touch.position);
            touchPosition.z = 0;
            direction = (touchPosition - transform.position);
            rb.velocity = new Vector2(direction.x, direction.y) * moveSpeed;
            GetComponent<BoxCollider2D>().enabled = false;

            if (touch.phase == TouchPhase.Ended)
                rb.velocity = Vector3.zero;
        }
        else
        {
            GetComponent<BoxCollider2D>().enabled = true;
        }
    }

    private void OnMouseDown()
    {
        go = gameObject;
    }
}