Possible means it can be done. Plausible means it could be possible, but there is some degree of uncertainty to it. 1. I can walk to the convenience store near my house. 2. My birthday is in 30 days. I want to visit all 50 states before my birthday. I have 30 states left to visit to make this happen. In sentence 1, we could find out that the distance to the store is only a few blocks from the house. This then can be stated as possible since the distance is so short. In sentence 2, if I had enough money and there were no restrictions on travel, this could be possible. Given the current state of travel restrictions, this is unlikely to happen. But travel restrictions could lift and I could still manage to achieve that goal. But, we do not expect the travel restrictions to change. So, while it is possible under the right set of conditions, this goal does not appear to be possible right now. So, it is plausible that it could happen, although only under certain conditions that are not likely to occur.

Possible = not impossible, something that can happen. Plausible = reasonable, believable, something that (it is thought) will likely happen; feasible, achievable. Everything that is deemed plausible is also assumed to be possible (even if that is not necessarily the case), but of course that which is possible may not seem plausible. Plausible stuff requires someone believing in it and implies a higher probability, whilst possible stuff is rather objective and usually implies a certain remoteness. Furthermore, possible also may mean achievable (used in contexts where considering plausibility seems irrelevant). i. Hers is a plausible (believable) alibi. ii. Yes, sure, a few people have visited the moon, so it's possible that you have been there. But do you really expect me to believe it? iii. Do you think it's still possible for me to (that I still can) get into Harvard?