Mach 1 is the speed of sound, which varies by the air's pressure and temperature. Mach 1 at sea level is 340.3 m/s, 761.2 mi/h, 1,225 km/h
http://wiki.answers.com/Q/How_Fast_is_a_Mach

In the Trophosphere, Mach 1 is 799.5 mph, Mach 2 is 1599 mph, and M...
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Mach 1 is the speed of sound, which is 332 m/s or 1195 km/hr or 717 miles/hour. Mach numbers are named after an Austrian philosopher, Ernst Mach (18381916).
http://www.kgbanswers.com/howfastismach1/42235...

1. Measure the temperature for which you want to make your conversion. For example, you use a temperature of 40 degrees Fahrenheit. 2. Add 460 to your temperature to convert your
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