Question

Why different unit of speed is used to measure the speed of a ship and a motor vehicle?

Answer 1

Do you mean knots?

Answer 2

take the example of a ROM in computers:u address them in terms of Giga Bytes rather than KiloBytes...its because the small value (say 500GB is easier to scale and convey, compared to 500*2^20 KB).so in the same sense,we have different ways of measuring speed.