Answer:
The length of the string is 0.051 meters
Step-by-step explanation:
It is given that,
Tension in the string, T = 240 N
Mass of the string, m = 0.086 kg
Speed of the wave, v = 12 m/s
The speed of the wave on the string is given by :

M is the mass per unit length of the string i.e. M = m/l.......(1)
So,


M = 1.67 kg/m
The length of the string can be calculated using equation (1) :


l = 0.051 m
So, the length of the string is 0.051 meters. Hence, this is the required solution.