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## Homework Statement

Piano wire weighs 77kN/m^3 and breaks at a stress of 3000MPa. Calculate the length of piano wire that can be lowered down a very deep mine before it breaks.

## Homework Equations

stress = force/area

## The Attempt at a Solution

Piano wire = 77 000N/m^3

stress = 3000 000 000Pa(N/M^2)

Area of cross section = (pi)(d^2)/4

Force exerted by x m^3 of piano wire is (x)(77000)

Therefore

3 000 000 000 = (4)(77000)(x) /(pi)(d^2)

ASSUME d = 0.0002m

x = 0.122399m^3

Volume = (pi)(r)^2 * h

0.122399 = (pi)(0.001)^2 * h

h= 38 960

This seems a bit too much.

My professor is known for throwing out questions that require "engineering intuition for making assumptions."

Not sure if my solution is right or I can do it without making an assumption.

This is a problem set, no solutions please but only tell me if I'm way off (or close and where i made the mistake).

I appreciate it.