Question

Two tuning forks $A$ and $B$ made of same material are slightly out of tune and produce beats of frequency $7\text{Hz}$. When $B$ is slightly filed, the beat frequency increases to $9\text{Hz}$. If the frequency of $A$ is $274\text{Hz}$, the original frequency of $B$ was

• A. $524\text{Hz}$
• B. $268\text{Hz}$
• C. $281\text{Hz}$
• D. $312\text{Hz}$

Answer 1

The correct option is C $281\text{Hz}$

As beat frequency increases on filing $B$

$f_A<f_B\Rightarrow f_B-f_A=7\Rightarrow f_B=f_A+7$

$=274+7=281\text{Hz}$