A high elf and a mountain dwarf stand on the edge of a 150' chasm. They are without modification to their racial speeds, so the elf moves at 30' and the dwarf moves at 25'.
Two ropes are anchored above the chasm, fixed in such a way as to allow a medium creature to swing from one side of the chasm to the other.
They grab the ropes and swing, arriving safely on the other side.
How long, by the rules, does it take them to get there?
Is it speed determined?
If it is speed determined, then the elf gets there in 5 rounds and the dwarf gets there in 6. I suppose if Dash is applicable, they get there in half that time.
But that doesn't make much sense, because speed is a characteristic describing how fast something moves, moving under its own power, or as a result of its own power.
Is it physics determined?
If it's physics it's pretty iffy. Magic is so much more reliable! But on earth it would be the square root of the length of the pendulum in meters (thanks Dale M.), so in this case we wouldn't know because the length of the rope isn't given, but it would be the same length of time for both the dwarf and the elf.