How to add force based on distance of mouse position

 

using UnityEngine;

public class ShootSanta : MonoBehaviour {

    bool used = false;

    public Rigidbody2D rb;
    public Collider2D cl;

    void Start()
    {
        rb = GetComponent<Rigidbody2D>();
        cl = GetComponent<Collider2D>();

        rb.gravityScale = 0;
    }

    void FixedUpdate()
    {
        var mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        var mouseDir = mousePos - gameObject.transform.position;
        mousePos.z = 0.0f;
        mouseDir = mouseDir.normalized;

        if (Input.GetMouseButtonDown(0) && used == false)
        {
            rb.gravityScale = 1;

            rb.AddForce(mouseDir * 1500);

            used = true;
        }

   
    }

}