A hollow pipe of length 0.8 m is closed at one end. At its open end a 0.5 m long uniform string is vibrating in its second harmonic and it resonates with the fundamental frequency of the pipe. If the tension in the wire is 50 N and the speed of sound is 320 ms−1 , find the mass of the string.
(1) 5 grams
(2) 10 grams
(3) 20 grams
(4) 40 grams