How many mph does an object have to go in order to break the sound barrier

Well, it's kind of a slippery number, because the speed of sound
depends on the air that the sound is traveling through, so it's actually
different for different aircraft flying at different altitudes, where the
pressure, temperature, and density of the air are different.

Here are some "standard" values"

On the ground . . .  761 mph

10,000 feet            733 mph

20,000 feet            705 mph

30,000 feet            677 mph

50,000 feet            660 mph

100,000 feet          676 mph
 

Earthplanet yplanet y5=earth     *many different equationsplanet x1.5=earthplanet x is two times planet yobject 5,2500 mass5,1,3,2,4object 1 is four times obect 4