Expressions

1. Assume that someone was lying on the ground injured

Would any of these expressions be appropriate to be used?

a) "Hang in there. I'm going to call for help."

b) "Hold on. I'm going to call for help."

Note: I should emphasize that the person is lying on the ground, and is not hanging or holding anything.

2. Now, assume that I'm speaking to someone to get their help, would it be correct to say:

a) "Jim was still alert when I came, but he certainly won't hang in there the whole time."

b) "Jim was still alert when I came, but he certainly won't hold on there the whole time."

Note: Can those expressions be used, even if not in the imperative form.