Misc: who composed the 'blue danube waltz'?

Questions

what is the speed of a body expressed as a ratio with the speed of sound?

what measure is used for the purity or fineness of gold?

what is the name of the instrument that is used to test the level of charge in a car battery?

what is the name given to the side opposite the right angle of a right-angled triangle?

what is a vein or fissure in a rock containing mineral deposits called?