Question

Two tuning forks $A$ and $B$ produce $4beats/sec$. Forks $B$ and $C$ produce $5beats/sec$. Forks $A$ and $C$ may produce ________ beats/ sec.

• A. $5$
• B. $9$
• C. $20$
• D. $2$

Answer 1

The correct option is B $9$

We consider two possible cases about tuning forks $A,B$ and $C$,
Case I When $A$ and $B$ are tuned, four beats are produced. When $B$ and $C$ are tuned, five beats are produced.
So, there is a difference of $1$.
Case Ii When $A$ and $C$ are tuned, the total number of beat produced is 9.