Speed after Vector3.Reflect Decreases,Speed of ball after Vector3.Reflect decreases

I have a Ball and A Surfboard. When the ball collides with the Surfboard, the Speed of the ball decreases. The decrease in speed is evident by seeing it in game mode.

I use rigidbody velocity in start() multiplied by the speed of ball; I change the rigidbody velocity in another function in the script attached to ball after it is called from the script of Surfboard after collision.

Here's the code:

Surfboard script -

using System.Collections;

using System.Collections.Generic;

using UnityEngine;

public class SurfBoard : MonoBehaviour

{

 [SerializeField]

 private float _speed = 3.5f;

 private SurfBall _surfBall;

 // Start is called before the first frame update

 void Start()

 {

     transform.position = new Vector3(0,0,0);

     _surfBall = GameObject.Find("Surf Ball").GetComponent<SurfBall>();

     if(_surfBall == null){

         Debug.LogError("The Surf Ball in NULL");

     }

 }


 // Update is called once per frame
 void Update()
 {
     float horizontalInput = Input.GetAxis("Horizontal");
   float verticalInput = Input.GetAxis("Vertical");

   transform.Translate(new Vector3(0,1,0) * horizontalInput * _speed * Time.deltaTime);  
   
   transform.Translate(new Vector3(1,0,0) * verticalInput * _speed * Time.deltaTime); 
 }

 private void OnCollisionEnter(Collision other) {
     if(other.gameObject.tag == "Surf Ball"){
         Debug.Log("collision Surf Ball");
         Vector3 SurfBoardNormal = other.GetContact(0).normal;
         _surfBall.BallSpeed(SurfBoardNormal);
     }
 }
     

}

Ball script -

using System.Collections;

using System.Collections.Generic;

using UnityEngine;

public class SurfBall : MonoBehaviour

{

 [SerializeField]

 private float _ballSpeed = 1f;

 [SerializeField]

 private Rigidbody _rb;

 // Start is called before the first frame update

 void Start()

 {

     transform.position = new Vector3(3,4,0);

     _rb = GetComponent<Rigidbody>();

     _rb.velocity = new Vector3(-1,-1,0) * _ballSpeed;

 }


 // Update is called once per frame
 void Update()
 {

 }

 public void BallSpeed(Vector3 Normal)
 {
     _rb.velocity = Vector3.Reflect(_rb.velocity,Normal);
 }

}

What Should I Do?

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