This article explains how to force quit an iPad app on devices running iOS 7 and later.
How to Force Quit an App on iPad and iPhone
If you want to quit an app because it's behaving strangely, or if you suspect the app is causing other problems, such as slowing down your iPad, then clicking the Home button won't do any good.
To force an app to quit, open the multitasking and controls screen. To get there, double-click the Home button at the bottom of your iPad. (If your iPad doesn't have a Home button, swipe up from the bottom of the Home screen.) The Home button is the physical button just below the iPad's screen that's used for Touch ID.
The App Switcher appears with your most recently opened iPad apps as panes across the screen. Each pane has an icon above it, along with its name. Swipe left to right to scroll through new apps, so you can still get to them if the app in question isn’t the most recently used.
