One tuning fork vibrates at 440 Hz, while a second tuning fork vibrates at an unknown frequency. When both tuning forks are sounded simultaneously, you hear a tone that rises and falls three times per second. What is the frequency of the second tuning fork?

Explanation:

On sounding two tuning forks together , we hear beats which is heard at a rate equal to difference of frequencies of tuning forks.

In the present case too , beat is heard .

Frequency of beat heard = 3

The frequency of second tuning fork must be higher by 3 or lower by 3

So the possible frequencies of vibration of unknown tuning fork= 440 +3 or 440 - 3

443 Hz

or , 437 Hz .

443 Or 437 is the answer.