I can't update my speed after reaching certain score

My score class

 using UnityEngine;
 using System.Collections;
 
 public class Score : MonoBehaviour {
 
     public GUIText scoreText;
 
     public int scoreStart = 0; 
 
 
     public void scoreUpdate(){
 
         scoreStart++;
         scoreText.text = "Score: " + scoreStart;
         //Debug.Log ("The updated score is "+scoreStart);
         
         }
 
     public void OnTriggerEnter (Collider col){
 
         if (col.gameObject.tag == "Bullet") {
             //Debug.Log ("Player hit");
             scoreUpdate();
             }
 
         if (scoreStart == 10) {
             Debug.Log ("update speed");
             col.GetComponent<Bullet>().updateSpeed(100f);
                 }
         }
 
 }
 

My bullet class in which I want the speed to be updated

 using UnityEngine;
 using System.Collections;
 
 public class Bullet : MonoBehaviour {
     
     private float bulletSpeed;
 
     void Start () {
         bulletSpeed = 10f;
 
         }
 
     public void OnTriggerEnter(Collider col){
         if (col.gameObject.tag == "Player") {
             Debug.Log("Player get hit");
             Destroy(gameObject);
         }
         
     }
     // Update is called once per frame
     void Update () {
         transform.Translate(Vector3.right * -1 * Time.deltaTime * bulletSpeed);
         Debug.Log ("current speed: " + bulletSpeed);
 
     }
 
      public void updateSpeed (float speed){
         
         bulletSpeed += speed;
         Debug.Log ("Upgraded Speed: " + bulletSpeed);
     }
     
 }