The speed of a mechanical wave depends on the mechanical properties
of the medium through which the wave is traveling.
The speed of an electromagnetic wave depends on the electrical properties
of the medium through which the wave is traveling.
It's pretty well unanimous for choice <em>A</em> .
“The term significant figures refers to the number of important single digits (0 through 9 inclusive) in the coefficient of an expression in scientific notation . The number of significant figures in an expression indicates the confidence or precision with which an engineer or scientist states a quantity.”
The difference between velocity and relative velocity is that velocity is measured with respect to a reference point which is relative to a different point. While relative velocity is measured in a frame where an object is either at rest or moving with respect to the absolute frame.
It depends who is watching it.
-- A passenger on the train says that his clock is normal, but the clock at the station he just passed is running slow.
-- A ticket agent at the station says that his clock is normal, but the clock on the train that just rolled through is running slow.
-- They're both correct, but ...
-- The difference is too small for either of them to notice, unless the train is going faster than about half the speed of light.
-- It isn't.
