Question

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

• A. 2
• B. 5
• C. 9
• D. 20

Answer 1

Answer: (C)

9

Answer 2

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

$\left|n_{A}-n_{C}\right|=1$
Case II When $A$ and $C$ are tuned, the total number of beat produced.

$\left|n_{C}-n_{A}\right|=4+5=9$