A heavy string is tied at one end to a movable support and to a light thread at the other end as shown in figure. The thread goes over a fixed pulley and supports a wieght to produce a tension. The lowest frequency with which the heavy sting resonates is `120 Hz`. If the movable support is pushed to the right by `20 cm` so that the joint is placed on the pulley, what will be the minimum frequency at which the heavy string can resonate?

Answer

240 Hz

Explanation

Initiallly because the end A is free and antinode will be formed.
`So, I=lambda_1/4` Again if the movable support is pushed to right by 10 m, so that the joint is placed on the poulley, node will be formed there
So, `I=(lambda)/2`
Since the tension remains same in both the case, velocity remains same as the wavelength is reduced by half the frequency will become twice as that of 120 Hz i.e. 240 Hz.