Gravity, as we know, is an incredibly weak force. So weak that it takes a whole lot of stuff in one place for its effects to become noticeable.
So, how much, really?
Let’s postulate that our planetoid has roughly the same density as the Earth, and is perfectly spherical; no high places to jump from. Let’s also postulate that I am a 165-lb. (~75kg) Olympic athlete who can run and jump with the best of them. And finally, let’s postulate that my life-support equipment doesn’t hinder my motion in any significant way. (After all, if this planetoid’s gravity is just barely strong enough to keep me down, it’s not going to have an atmosphere to speak of. If necessary for the problem, assume no atmosphere at all.)
So, how big does the planetoid have to be, to make sure that if I go up, I come back down?
Along the same lines, suppose I can drive a golf ball as well as anyone the PGA Tour has ever seen. How big does the planetoid have to be so that my golf ball must resurface, so to speak?