Error AddForce: error CS0117: 'UnityEngine.Gameobject' does not contain a definition for 'AddForce

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

 public class shooting2 : MonoBehaviour {
     public Rigidbody2D bulletPrefab;
     public Transform barrelEnd;
     public float timeBetweenShots = 0.33333f;
     float timestamp;
 
     void Start () {
     }
 
 
     void Update () {
         if (Time.time >= timestamp && (Input.GetKey (KeyCode.Space)) ){
             GameObject bulletInstance;
             bulletInstance = Instantiate (bulletPrefab, barrelEnd.transform.position, barrelEnd.rotation) as GameObject;
             bulletInstance.UnityEngine.Gamobject (barrelEnd.forward * 5000);
             timestamp = Time.time + timeBetweenShots;
         }
     }
 }

bulletInstance.GetComponent().AddForce( barrelEnd.forward * 5000 );