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

As end `A` is free so antinode is formed
`:. l = (lambda_(1))/(4)`
Now if support is pushed to right by `10 cm` so that node is formed at joint
`:. L = (lambda)/(2) rArr (lambda_(2) = (lambda_(1))/(2))`
As `V` is same so if wavelength is halfed frequency will be doubled i.e. `240 Hz`