What is the frequency of unknown tuning fork

[lauralovesyou]

Homework Statement

A tuning fork w/ frequency of 256 Hz sounded w/ another tuning fork w/ unknown frequency produces 30 beats in 10 seconds. Then, one tine is covered in plasticine and sounded again w/ the unknown frequency tuning fork and produces 20 beats in 10s. What is the frequency of unknown tuning fork.

Homework Equations

BF= #beats/total time=f1-f2
= 30/10
= 3 Hz
= 256+/-3 Hz
= 253 or 256 Hz

That's all I got to, I don't know how to use the info from second piece of information to find exact frequency?

 

[aim1732]

You make an assumption that either the unknown or known frequency is greater (your discretion). Then you analyse whether in the beat freq. should increase or decrease if frequency of one the forks is altered. If it does then your assumption is correct otherwise you go for the other frequency you had in your answer. In this case the known freq. decreases.