You should be able to close an unresponsive App by swiping it off the top of the screen from the App Switcher.
- To quit an app, open the App Switcher, then swipe up on the app.
- To reopen the app, go to the Home Screen, then tap the app.
If quitting and reopening the app doesn’t solve your problem, try restarting iPad.
Quit and reopen an app on iPad - Apple Support
Be aware that fully closing an App does not reduce battery use - but actually increases battery consumption. Fully closing and subsequently re-launching an App is the least power-efficient method of managing running Apps.
Once initially launched, iOS Apps are generally in one of four states:
- The App is “Active” - it is running running in the foreground. When you switch tasks, the App will continue to run in active state for some minutes before its resources are released and is placed into an Inactive state.
- The App is “Inactive” but remains loaded in [fast] RAM. In this state, the App can be instantly restored to an Active state - but is not consuming CPU or other resources whilst in the inactive state.
- The App is “Inactive” and unloaded. In this state, the App has been completely offloaded (releasing RAM for use by other processes) but its running state has been saved to [slow] flash memory. Returning to an App in this state will cause the App’s saved state to be efficiently reloaded from flash memory into Active RAM - without the need to re-initialise the App.
- The App has been closed. All running data has been expelled - there is no “saved” state; relaunch will reload and re-initialise the App from scratch.
Memory management is generally a juggling act - and for the most part, you should allow the OS to manage its memory space. Re-initialising an App is the slowest and most power hungry method of launching an App. Inactive Apps do consume some system resources, but by design, the required system resources to maintain this state are insignificant.
Force-closing an App releases all resources. Whilst the mechanism exists to do so (and in rare circumstances manual intervention to terminate an App may be necessary), a force close reduces system performance.
I hope this insight and clarification proves to be helpful to your understanding.