Fundamental frequency  

L = Length of string,  T = Tension in the string

m = Mass per unit length (linear density), p = mode of vibration

Important Points

 (1) As a string has many natural frequencies, so when it is excited with a tuning fork, the string will be in resonance with the given body if any of its natural frequencies concides with the body.

(2) (i)

(3) If M is the mass of the string of length L,

where m = pr²r  (r = Radius, r = Density)