As we have mentioned, we would like to destroy the bullet after a certain time specified by the timeBeforeDestruction variable. Unity comes with a built-in function to destroy a game object after a delay, and once again the Start() function is the perfect place for such a thing. In fact, we just need to specify the game object to destroy (in this case the bullet itself), and the time. So, the Start() function at the end should be like the following:

    void Start() { 
        rigidBody = GetComponent<Rigidbody2D>(); 
 
        //Destroy the bullet if it didn't hit anything after 10 seconds 
        Destroy(gameObject, timeBeforeDestruction); 
    } 

If you were to place a bullet in the scene now and hit play, it would be destroyed after ten seconds, which is the default value for the timeBeforeDestruction variable.