Well, a 2x4 on edge is 3 1/2" and a 2x10 is 1 1/2" thick making 5".
If you're talking about a ramp that would allow you to back the trailer from the road to the top of a 5" high sidewalk that'll do fine. Make the 2x10 a couple or feet or more long.
If that's not what you're trying to do, post a photo of the situation.
If you ripped a 4 foot by 8 foot sheet of 3/4" thick plywood into six 8-foot-long strips of different widths, you could build an 8-foot long (along the curb) ramp about a foot wide at the base, almost 5" high, with 3/4" high steps a couple of inches apart, which would be easier to pull a trailer over than 2" steps.
Ready-made ramps are sold, but offhand I don't know where.