Question

When an object moves with supersonic speed, the ratio of speed of object to that of sound is called: 

1. Mach number
2. Magic number
3. f-number
4. Reynolds number

Answer 1

Correct Answer - Option 1 : Mach number

Concept:

• Shock waves: When an object moves with a velocity greater than that of sound, it is termed as Supersonic.
• When such a supersonic body or plane travels in air, it produces energetic disturbance that moves in the backward direction and diverges in the form of a cone.
• Such disturbance is called the shock waves. 
• The speed of supersonic is measured in Mach number.
• One mach number is the speed of sound and it defined as the ratio of the velocity of the source to the velocity of sound i.e.,
   

\(Mach\;Number = \frac{{Velocity\;of\;source}}{{Velocity\;of\;sound}}\)

Explanation:

So these are the ratios of different speed of the body, for

1. Hypersonic > 5.0 mach
2. Supersonic > 1 mach
3. Subsonic < 1 mach

Hence, when an object moves with supersonic speed, the ratio of speed of an object to that of sound is called mach number.