A steel wire in a piano has a length of 0.8000 m..?

Question

A steel wire in a piano has a length of 0.8000 m and a mass of 5.000 10-3 kg. To what tension must this wire be stretched in order that the fundamental vibration correspond to middle C (fC = 261.6 Hz on the chromatic musical scale)?

Answer 1

One of the few cases where wikipedia let me down, but a simple Yahoo search on "violin string frequency" found:
http://hyperphysics.phy-astr.gsu.edu/hbase/waves/string.html

which has your answer.