A centrifugal pump is directly couple to a motor. The pump rating is 3,600 liters per minute against a total head of 8 meters of water. Pump efficiency is 65% at shaft speed of 550 rpm. Calculate the torsional stress induced on the 40 mm diameter motor shaft.

a)11,193.45 kPa

b)12,420.72 kPa

c)10,010.85 kPa

d)13,113.83 kPa