Convert Object Rotation to X, Y values

EDIT: I've cleaned up the scripts a little since I posted, hopefully they're a little easier to read. How do I convert the cannons rotation into the values I need for ballSpeedHorizontal and ballSpeedVerticle? Or am I going about this all wrong?

I have a cannon game object and I rotate the barrel of the cannon by holding a button. I'd like to shoot a cannon ball out of the cannon but the script I've created for the velocity of the ball needs x and y acceleration values. How can I convert the rotation amount of the cannon into the x and y acceleration values I need to get the ball to come out of the cannon at the correct angle? Here is the script I made for the cannon ball:

 using UnityEngine;
 using System.Collections;
 
 public class CannonBall : MonoBehaviour {
 
     public float ballSpeedHorizontal;
     public float ballSpeedVerticle;
 
     // Use this for initialization
     void Start ()
     {    
         //Give the cannon ball a velocity and direction when intsantiated
         rigidbody2D.velocity = new Vector3(-ballSpeedHorizontal, ballSpeedVerticle, 0);
 
         //Wait three seconds after instantiation and destroy the cannon ball
         Destroy(GameObject.Find("CannonBall(Clone)"), 3);
     }
     
     // Update is called once per frame
     void Update ()
     {    
 
     }
 }

And here is the script I made for the cannon:

 using UnityEngine;
 using System.Collections;
 
 public class CannonShoot : MonoBehaviour
 {
 
     public GameObject CannonBall;            // Cannon ball object
     public bool isShooting;                    // Should we shoot the ball
     Animator shootAnimator;                    // Cannon animato
 
     // Use this for initialization
     void Start ()
     {
         shootAnimator = GetComponent<Animator>();
     }
 
     //Spawn the cannon ball
     void SpawnBall ()
     {
         Instantiate(CannonBall, BarrelTip.tipLocation, Quaternion.identity);
     }
 
     // Update is called once per frame
     void Update ()
     {
         //Press Space to shoot a cannon ball
         if (Input.GetKeyDown ("space"))
         {
             ShootBall();
         }
 
         //Press A to rotate counter clockwise
         if (Input.GetKey ("a"))
         {
             //print ("Rotating Counter Clockwise!");
             transform.Rotate(0, 0, Time.deltaTime*100);
         }
 
         //Press S to rotate clockwise
         if (Input.GetKey ("s"))
         {
             //print ("Rotating Clockwise!");
             transform.Rotate(0, 0, Time.deltaTime*-100);
         }
     }
 
     //Trigger the ball shoot animation and print to screen
     void ShootBall ()
     {
         print ("We shot a ball!");
         shootAnimator.SetBool("isShooting", true);
         SpawnBall();
     }
 
     //Reset the cannon to it's idle position
     void ResetCannon ()
     {
         print ("We reset!");
         shootAnimator.SetBool("isShooting", false);
     }
 }