Can a jet-ski go 90 mph?

Answer 1

Depends on what you mean by "can". There's no physical or engineering limit preventing those speeds, but I don't think that any stock jet ski will be that fast. It'd be quite dangerous and difficult to control at those speeds and if you fell off, you'd lose an awful lot of skin. By law in the United States, jet skis cannot operate above 68 miles per hour. The world record is over 100 miles per hour.