Woman on Man rape can occur in situation where the woman has an authority over the man. Yes, most women are physically weaker than men, though if there's an age difference, weapons or some kind a manipulation involved, then it can easily be done. Let's say a woman is the boss of the man she decides to rape, his job is necessary in order for him to make a living and maybe to provide for his family. The boss makes it clear that if he refuses to do as she wishes, then he'll get sacked. This man doesn't want to, he loves his wife and family, and he's not sexually interested in his boss, but in the end, he is pressured into it. It leaves him emotionally scarred with shame and guilt. The boss says they need to continue their arrangement (her raping him) or that she'll press charges against him and tell his family of their "affair".
This can and has happened before, guys.