Solució: \begin{align} m &= \cssId{Step1}{ \frac {2·p_int·π·(\frac {d_int}{2})^2}{g}}\\[3px] &\cssId{Step2}{m= \frac {2·3,14·2,5·10^6·(\frac {0,1}{2})^2}{9,81}= 4004 kg} \\[3px] \end{align}