# Question #85ba3

##### 1 Answer

The fundamental frequency of a streched string is given by the follwing formula.

#n=1/(2l)sqrt(T/m)#

Where

So T and m remaining constant

#nprop1/l#

let the frequency of the string is

Si by the law of length

#n_1/n_2=21/20#

Let the frequency of tuning fork be

So

So

Again

Adding (1) and (2) we get

Inserting the value of x in (2)

#n_f-20*20=10#

#n_f=410Hz#