\(f _{2}= f +4\)
\(f _{3}= f +2 \times 4\)
\(f _{4}= f +3 \times 4\)
\(f _{20}= f +19 \times 4\)
\(f +(19 \times 4)=2 \times f\)
\(f =76 \; Hz\)
Frequency of last tuning forks \(=2 \; f\)
\(=152 \; Hz\)
(તારનો યંગ મોડ્યુલસ $Y =9 \times 10^{10}\, Nm ^{-2}$ )