At what frequency we can't the sound of vibra-tions of a pendulum ?

Options

A. Less than 20 Hz
B. More than 20 Hz
C. 20 Hz
D. None of them

Answer

To determine at what frequency we can't hear the sound of the vibrations of a pendulum, we need to understand the concept of frequency and the audible range of sound for humans.

### Step-by-Step Solution:

1. **Understanding Frequency**:
- Frequency is defined as the number of oscillations or vibrations that occur in one second. It is measured in Hertz (Hz).

2. **Audible Range**:
- The human ear can typically hear sounds within a frequency range of 20 Hz to 20 kHz (20,000 Hz). Sounds below 20 Hz are considered infrasonic, and sounds above 20 kHz are considered ultrasonic.

3. **Identifying Frequencies**:
- If the frequency of the pendulum's vibrations is less than 20 Hz, it falls into the infrasonic range, which is not audible to humans.
- Therefore, any frequency below 20 Hz will not be heard by the human ear.

4. **Conclusion**:
- The frequency at which we cannot hear the sound of the vibrations of a pendulum is any frequency that is less than 20 Hz.

### Final Answer:
We cannot hear the sound of the vibrations of a pendulum at frequencies less than 20 Hz.

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