A prestressed concrete beam of$$a rectangular section is $150$ mm wide, $375$ mm deep, and is simply supported throughout$8$ meters.$$The$$beam is concentrically prestressed by a cable carrying an effective prestressing force is$337\mathrm{.}50$ KN$.$ The beam supports an all$-$inclusive load of$8$ KN$/$m$.$ Compare the principal tensile stresses induced in the beam with and without the prestress, at the support section.