How do I get ball to go the same speed for the game Pong?

Here is My Script using UnityEngine; using System.Collections;

public class Ball : MonoBehaviour {

 public float ballVelocity = 3000;
 
 Rigidbody rb;
 bool isPlay;
 int randInt;

 void Awake ()
 {
     rb = gameObject.GetComponent<Rigidbody> ();
     randInt = Random.Range(1, 3);
 }
 
 
 void Update ()
 {
     if(Input.GetMouseButton(0) == true && isPlay == false)
     {
         transform.parent = null;
         isPlay = true;
         rb.isKinematic = false;
         if (randInt == 1)
         {
             rb.AddForce(new Vector3(ballVelocity,ballVelocity,0));
         }
         if (randInt == 2)
         {
             rb.AddForce(new Vector3(-ballVelocity,-ballVelocity,0));
         }
     }
 }

}