I have a flight with Emirates to LAX and then a flight with United. If I arrive at 1:55 pm at LAX and my next flight is at 2:50 pm, is there enough time? Both flights are international.
No. United and Emirates do not interline, so the only way this connection could happen would be if you purchased two separate tickets. This is not nearly enough time for that.
When you arrive in LAX on an international flight from Dubai, you'll have to go through US immigration and customs, change terminals, then security, then to your gate. And if you have checked luggage, you'll have to pick it up and check it in at the United counter. 55 minutes is not nearly enough time for that. You could be in immigration longer than 55 minutes (you can check past wait times online). Worse, you're required to check your bags at least an hour before departure, and that's entirely impossible.
In addition, if you book two separate tickets, you are responsible for your own connection, not the airlines. If you miss the flight (and in this case, you will), the airline has no obligation to help, and you could have to shell out a lot of cash at the last minute for a replacement ticket. I'd encourage you to buy this trip as a single ticket instead, or at least to leave a long buffer between flights if you're sure you want two separate tickets.
If it is on two separate tickets, it is impossible. Your luggage must be checked in with the second airline one hour before the flight (international two hours), and you will be still in the air that time.
You need a minimum of three hours to go through immigration and customs, and still be two hours before the next flight to check you luggage. Unless you don't care about the cost to buy a new ticket in the fly, plan a minimum of five hours, better more.
If you have no luggage, and you fly business class, you have a 50/50 chance to make it in time, assuming your flight doesn't come in late.
If you have it booked on one ticket, it is the airlines problem. They will simply rebook you on a new connection; if you don't care to arrive a day late, it will be ok.