I have a general query about velocity of waves. We have a formula velocity of waves V = fλ ; f= frequency,λ= wavelength But in string waves it's V = √(F/μ) ; where F is tension force μ=linear mass density. I am confused with other formulas also(like sound wave velocity). Is the V = fλ the general one , i.e we can use it in any case either sound wave or string. And then what is the need of the second formula above.