In a porter governor, the upper and lower arms are each 250mm long and pivoted on the axis of rotations. The mass of each rotating ball is 3 kg and mass of the sleeve is 20 kg. The sleeve is in its lowest positions when the arms are inclined at 30° to governor axis. The lift of the sleeve is 36 mm. Find the force of friction at the sleeve, if the speed at the moment it rises from the lowest position is equal to the speed at the moment it falls from the highest position. Also, find the range of speed of the governor.