The ratio of the speed of a body to the speed of sound is known as

Options

A. refractive index
B. mach number
C. relative density
D. none of these

Answer

To solve the question, "The ratio of the speed of a body to the speed of sound is known as," we will follow these steps:

### Step 1: Understand the Concept
We need to identify the term that describes the ratio of the speed of a moving object (body) to the speed of sound in the medium through which it is traveling.

### Step 2: Define the Terms
- **Speed of a Body (v)**: This is the velocity at which the object is moving.
- **Speed of Sound (c)**: This is the speed at which sound waves travel through a particular medium (like air, water, etc.).

### Step 3: Write the Ratio
The ratio can be mathematically expressed as:
\[ \text{Ratio} = \frac{\text{Speed of the Body}}{\text{Speed of Sound}} = \frac{v}{c} \]

### Step 4: Identify the Name of the Ratio
This ratio is known as the **Mach number**. The Mach number is a dimensionless quantity used in fluid dynamics to represent the speed of an object relative to the speed of sound in the surrounding medium.

### Step 5: Conclusion
Thus, the answer to the question is that the ratio of the speed of a body to the speed of sound is called the **Mach number**.

### Final Answer
The ratio of the speed of a body to the speed of sound is known as the **Mach number**.

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