The inner (inlet) and outer (outlet) diameters of the impeller of a centrifugal pump are 200 mm and 400 mm. The pump runs at 1200 rpm. The vane angles at inlet and outlet are 20° and 30°. Water enters the impeller radially and the velocity of flow is constant. Determine the work done by the impeller per unit weight of water (answer in N·m/N).