How to show velocity of prefab in scene?

I am making a projectile game and want to display its instant velocity in the game. For this I am using following approach:

1. Instantiate ballProjectile prefab whenever a shoot button is pressed with some velocity.

2. Display velocity of ballProjectile using UI.Text element.

But I am not able to do this as velocity is not updated in every frame.

My code is

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class ProjectileFlow : MonoBehaviour {
 
     public Rigidbody2D asteroidProjectile ;
     public float speed = 10;
     public Text range, height, velocityX, velocityY;
     public float fireAngle; 
 
     private Vector3 instantVel; 
     private float vY, vX;
 
     void Start()
     {
         transform.Rotate (new Vector3 (0,0 , fireAngle -30));
         vY = speed * Mathf.Sin (fireAngle * Mathf.Deg2Rad);
         vX = speed * Mathf.Cos (fireAngle * Mathf.Deg2Rad);
     }
     
 
     void FixedUpdate () {
 
         vY = speed * Mathf.Sin (fireAngle * Mathf.Deg2Rad);
         vX = speed * Mathf.Cos (fireAngle * Mathf.Deg2Rad);
         
         if (Input.GetKeyDown(KeyCode.A)) {
             ThrowProjectile();
         }
 
         if (Input.GetKeyDown (KeyCode.R)) {
             Application.LoadLevel(Application.loadedLevel);
         }
         
         updateValues ();
     }
 
     public void ThrowProjectile()
     {
         Rigidbody2D asteroidClone = (Rigidbody2D) Instantiate(asteroidProjectile, transform.position, transform.rotation);
         asteroidClone.velocity =  new Vector3(vX, vY, 0);
         instantVel = asteroidClone.velocity;
     }
 
     public void adjustSpeed(float newSpeed)
     {
         speed = newSpeed ;
     }
 
     public void adjustAngle(float newAngle)
     {
         fireAngle = newAngle;
         transform.Rotate (new Vector3 (0,0 , fireAngle -30));
         transform.eulerAngles = new Vector3(0, 0, fireAngle -30);
     }
 
 
     void updateValues()
     {
         velocityX.text = "Vx: " + instantVel.x.ToString();
         velocityY.text = "Vy: " + instantVel.y.ToString();
     }
 
 }