Question

The disc of the siren containing 60 holes rotates at constant speed of 360 rotations per minute. The emitted sound is in unison with a tuning fork of frequency:
A. 270 Hz
B. 360 Hz
C. 480 Hz
D. 540 Hz

Answer 1

Here we have been given a number of holes say, N=60 and constant speed say, S=360 rpm. And we are asked to find the frequency of the sound that will be in unison with a tuning fork of the same frequency. It means that frequency of sound waves produced by disc should be equal to frequency of a tuning force.

Complete step by step answer:
There are 60 holes on the given disc. Which means that after one complete 360 revolution of the disc no of waves produced will be equal to 60 in one revolution.
Now, let's write all the given values
N=60 and S=360 rpm
Now, as the speed is given in revolutions per minute(rpm), we should convert it into revolutions per second
Therefore,
$S=\dfrac{360}{60}=6rps$
Now, we know frequency is given by,
Frequency = number of waves per second
Frequency = $60\times 6$
Therefore,
Frequency = 360Hz
Therefore, the correct answer is option B.

Additional Information:
This particular question can be tricky as not much data is given. But, we can solve this by thinking about what frequency is. Therefore, we must know that frequency is the number of cycles per second.

Note:
Frequency is the number of occurrences of a repeating event over time. The unit of frequency is hertz, Hz. One Hz equals one vibration per second. Tuning fork is a metal instrument with two prongs. A tuning fork can be used as a resonating actuator. In early days it was used by musicians to tune instruments.