[amp_mcq option1=”unity” option2=”greater than unity” option3=”greater than 2″ option4=”greater than 4″ correct=”option2″]
The correct answer is B. greater than unity.
Mach number is a dimensionless quantity representing the ratio of the speed of an object to the speed of sound in the fluid through which it is moving. For hypersonic flow, the Mach number is greater than unity, which means that the speed of the object is greater than the speed of sound.
Option A is incorrect because the Mach number is greater than unity for hypersonic flow.
Option C is incorrect because the Mach number can be greater than 2, but it does not have to be.
Option D is incorrect because the Mach number can be greater than 4, but it does not have to be.