In resonance column experiment a tuning fork of frequency `f = 400 Hz` is held above the pipe as shown in figure. The reservoir is raised and lowered to change the level of water and thus the length of the column of air in the tube. The area of cross section of the reservoir is 6 times that of the pipe. Initially, the reservoir is kept so that the pipe is full up to the brim. Tuning fork is sounded and the reservoir is lowered. When the reservoir is lowered by `21 cm`, first resonance is recorded. When the reservoir is lowered further by `49 cm` the second resonance is heard. Find the speed of sound in air.

Answer

`336 ms^(-1)`