Fly-wheel is used with an engine because it

Options

A. Increases the efficiency of engine
B. Converts linear motion into rotatory motion
C. Is computsory by law
D. Makes the motion smooth and cuts down the vibrations

Answer

To solve the question regarding the purpose of a flywheel when used with an engine, we can analyze the options provided and understand the function of a flywheel in mechanical systems.

### Step-by-Step Solution:

1. **Understanding the Function of a Flywheel**:
- A flywheel is a mechanical device that stores rotational energy. It is typically a heavy wheel that is mounted on an axle and is designed to maintain a consistent speed of rotation.

2. **Analyzing the Options**:
- **Option 1: Increases the efficiency of the engine**: While a flywheel can contribute to the overall efficiency of an engine by smoothing out power delivery, its primary function is not to increase efficiency directly.
- **Option 2: Converts linear motion into rotary motion**: This is not a primary function of a flywheel. Flywheels do not convert motion types; rather, they store energy.
- **Option 3: It computes by law**: This option does not relate to the function of a flywheel in any meaningful way.
- **Option 4: Makes the motion smooth and cuts down the vibration**: This option accurately describes the role of a flywheel. It helps to smooth out the power delivery from the engine and reduces fluctuations in speed and vibrations.

3. **Conclusion**:
- Based on the analysis of the options, the correct answer is **Option 4: Makes the motion smooth and cuts down the vibration**. The flywheel's inertia helps in opposing fluctuations in speed, providing a more stable and smooth operation of the engine.

### Final Answer:
A flywheel is used with an engine because it makes the motion smooth and cuts down the vibration.

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