Solució: \begin{align} m &= \cssId{Step1}{ \frac {mg}{2·π·(\frac {d_tija}{2})^2}}\\[3px] &\cssId{Step2}{m= \frac {4004·9,81}{2·3,14·(\frac {0,056}{2})^2}=7,972 MPa} \\[3px] \end{align}