# Fluid Mechanics - Mechanical Engineering (MCQ) questions and answers for Q. 4029

Q.  Square root of the ratio of inertia force to elastic force is called as
- Published on 05 Aug 15

a. Mach's Number
b. Cauchy's Number
c. Both a. and b.
d. None of the above

ANSWER: Both a. and b.

#### Discussion

• Pankaj   -Posted on 05 Oct 15
Square root of the ratio of inertia force to elastic force is called as Mach's Number or Cauchy's Number

MN = √(Inertia Force / Elastic Force)

= √((Mass x Acceleration) / (Elastic Stress x Area))

= √((ρ x V x A x V ) / (K x A))

= √((ρ x V2) / K)

MN = V / √(K / ρ)

Mach's Number or Cauchy's Number is applied in compressible fluid flow, problem at high speed such as high velocity flow in pipes, water hammer, motion of high speed object like aeroplane and missiles. In these conditions are predominant.

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