A wire is under tension of $2$ kg wt and a wave is travelling through it with some speed. Tension in the wire is so increased that the wave travels through it with thrice the original speed. The increase in tension is (in kg wt)

A Pipe open at one end has length $0.8$ m. At the open end of the tube a string $0.5$ m long is vibrating in its first overtone and resonates with fundamental frequency of pipe. If tension in the string is $50$ N, the mass of string is (Neglect end correction) (Speed of sound $= 320$ m/s)

A sonometer wire resonates with $4$ antinodes between the two bridges for a given tuning fork when $1$ kg mass is suspended from the wire. Using same fork, when mass M is suspended, the wire resonates producing $2$ antinodes between the two bridges. (Distance between the bridges as before) The value of M is

The fundamental frequency of sonometer wire is $50$ Hz for some length and tension. If the length is increased by $25\%$ by keeping the tension same, then the frequency change of second harmonic is