Answer:
Lowest frequency = 537.5 Hz
Third frequency=2687.5 Hz
Step-by-step explanation:
Given that
Length of pipe ,L= 16 cm
Speed of sound,V = 344 m/s
Also given that it behave like stopped pipe and we know that fundamental frequency for this type of system given as

Now by putting the values


Now second harmonic frequency



Now third harmonic frequency


