kill(all);

A:2*%pi*rm*t;

J:integrate((rm*cos(theta))^2*t*rm,theta,0,2*%pi);

Pcrit: i^2*%pi^2*E*J/l^2;

dim:[E=70000,l=400,rm=9.4,t=1.2];

Pcrit,dim,numer;

k:E*A/l;

Pcrit/k,dim,numer;