Question

A 256 Hz tuning fork is resonating in a closed tube on a warm day when the speed of sound is 346 m/s. What is the length of the closed tube?
A. 1.35 m
B. 0.74 m
C. 0.34 m
D. 0.18 m

Answer 1

Assuming our "closed tube" is closed at only one end, then 
 v = fλ = f*4L/n 
 where "n" is the harmonic number. So 
 L = nv / 4f = n*346m/s / 4*256Hz = n*0.38 m 
 Since the only option in your list that is an integer multiple of 0.38 m is 1.35 m
 I'd say that we're hearing the fourth harmonic. 
 answer is
 A. 1.35 m