Instantiate bullet hit enemy aim error

enemy trasnform not hit target. the enemy passes over the my fire script

 var enemy:Transform;
 var speed:float=0.2;
 var bullet:Transform;
 var bulletPivot:Transform;
 var distance:float=10;
 
 var fireRate:float=0.5;
 var i=fireRate;
 var fireDirection:Vector3=Vector3.zero;
 var fireSpeed:float=150;
 
 var fireAudio:AudioSource;
 
 function Update () {
 fireNow();
 }
 
 function fireNow(){
 var dist=Vector3.Distance(enemy.transform.position,transform.position);
     
     if (dist<distance){
         if(i>0){
             i-=Time.deltaTime;
         }
         
         if(i<=0){
         
             var bulletClone=Instantiate(bullet,bulletPivot.position,Quaternion.identity);
             
             fireDirection = enemy.transform.position-transform.position;
             
             bulletClone.transform.rigidbody.AddForce (fireDirection*Time.deltaTime*fireSpeed);
             
             i=fireRate;
             
             fireAudio.audio.Play();
         }
     
     
     
     }
 
 
 }