physics
posted by sandhu .
A vibrating stretched string has length 31 cm, mass 19 grams and is under a tension of 38 newtons. What is the frequency of its 3rd harmonic?
If the source of the wave is an open organ pipe of the same length as the wire, what would be the frequency of the 4 th harmonic?

How about showing that you have made some effort of your own? Find the appropriate equation in your course materials instead of expecting someone else to do it for you. Someone will gladly critique your work.
The formula will require that you know the wave speed in the wire. That is
V = sqrt[(Tension)/(linear density)]
= sqrt[38N/(.019kg/.31m)] = 24.9 m/s
The harmonic number is determined by how many halfwavelengths there are in the wire's standing wave pattern. For the frequency, you will use
F*(wavelength) = V