某弹簧不遵守胡克定律，若施力<img src="https://static.zxtiku.com/wangke/imgs/topic/348271cb61ddbc2c8da37dfa59bd699d.jpg"/>，则相应伸长为<img src="https://static.zxtiku.com/wangke/imgs/topic/7240c7951e929cba91cefbfcd67c05d9.jpg"/>，力与伸长的关系为<img src="https://static.zxtiku.com/wangke/imgs/topic/1fd18b17f7f38a1903bec7241c4f4a7d.jpg"/>求：将弹簧从定长<img src="https://static.zxtiku.com/wangke/imgs/topic/fc582c21f3763ab1dbfd7123d11970a6.jpg"/>拉伸到定长<img src="https://static.zxtiku.com/wangke/imgs/topic/f4565f57288c4d3719300cc8dff7b934.jpg"/>时所需做的功为_______ <img src="https://static.zxtiku.com/wangke/imgs/topic/86e664d1f493d3e915677d891292d112.jpg"/>.