How many miles per hour is mach 8?

Answer 1

Mach is not an absolute speed but a relative speed. The Mach value of an object is the ratio of the speed fo the object travelling through a medium to the speed of sound travelling through the same medium.

Now sound travels faster in denser mediums so the speed of sound in [dense]air at sea level is greater than the speed of sound at high altitude. So Mach 2 in the air at sea level is faster than Mach 2 at high altitude. But Mach 2 under water is very much faster.

However, most people are ignorant about the proper meaning of Mach and assume that it is simply related to the speed of sound at sea level at normal temperature/pressure/humidity - approximately 760 miles per hour. In that case Mach 8 would be 6080 mph.