Is it safe to join free wifi at hotels or hospitals?

Yes it is some what safe , but i advise you not to do any billing over it and you have to remember that it is a public WiFi connection. So just be careful on what you search and do. And no, your device wont get hacked or anything.

Any open and non-protected network is risky. I would recommend installing a VPN on your computer and enabling it when on an unprotected network.

If you only need a browser, then consider using Tor Browser when on unprotected networks.

Generally, yes, however it is normally an unsecure network, so I would not do any kind of secure surfing on it, such as banking, or credit card info, since it could be intercepted.