ANS:A - Mach

Inertial forces are obtained when the elastic forces are multiplied by the Mach number. The Mach number is a dimensionless quantity that expresses the ratio of the speed of an object (such as an aircraft or a fluid flow) to the speed of sound in the medium through which the object is traveling. In fluid dynamics, particularly in the study of compressible flows, the Mach number plays a significant role in determining the compressibility effects and the magnitude of inertial forces. Therefore, when elastic forces are multiplied by the Mach number, the resulting inertial forces account for the effects of compressibility and the speed of the flow relative to the speed of sound.