How do I make a projectile disappear seconds after it is fired? The projectile stays within the game forever. How do I disable it, 3 seconds after it has been fired?

Questions & Answers
1

var bullitPrefab:Transform;

function Update ()

{

    if(Input.GetKeyDown("e"))

    {

        var bullit = Instantiate(bullitPrefab, GameObject.Find("SummonEscape_Spawn").transform.position, Quaternion.identity);

        bullit.rigidbody.AddForce(transform.forward * 100);

    }

}

2 
function Update()
{

    if(Input.GetKeyDown("e"))
    {
    spawnBullet(grenade);
    }

}
var grenade;
spawnBullet()
{
    Instantiate(grenade, GameObject.Find("SummonEscape_Spawn").transform.position, Quaternion.identity);

    grenade.rigidbody.AddForce(transform.forward*100);
    yield WaitForSeconds(3);
    Destroy(grenade);
}

Not tested, but should work.