I have to be honest: I rarely hear "buck someone up." It's usually used as an imperative: C'mon, buck up! It's not that bad.
You usually say it (in my experience) when someone seems upset about something that should be easy to rebound from - like throwing a gutter ball or striking out in baseball. I wouldn't tell someone who just got out of the hospital to "buck up" for example.
3 is okay. That's physical.
Student or Learner