When you see a file ending in .part2.rar , it indicates that the game has been split into several smaller pieces. To successfully use this file, you must:

To ensure a secure and functional experience, it is highly recommended to download Call of Duty: Black Ops through official digital storefronts. This ensures you receive the full, uncorrupted game files and official support. Call of Duty: Black Ops on Steam

You cannot extract the game with just part 2. You need part 1, part 3, and so on, all located in the same folder.