ObstacleMovement.cs

using UnityEngine;
using System.Collections;

public class ObstacleMovement : MonoBehaviour {

    Transform tr;
    void Start () {
        tr = transform;
        tr.rigidbody2D.velocity = new Vector3(-GameManager.GameSpeed * 60, 0, 0);
    }


    void Update () {
        if(tr.position.x < -PlayerPrefs.GetFloat("CameraWidth"))
        {
            Destroy(tr.gameObject);
        }
        if (GameManager.GameSpeed == 0)
        {
            tr.rigidbody2D.velocity = Vector3.zero;
        }
    }
}