A centrifugal pump running at \(2,000 \mathrm{rpm}\) has internal and external impeller diameter of 250 \(\mathrm{mm}\) and \(350 \mathrm{~mm}\), respectively. The vane angles of the impeller at inlet and outlet are \(25^{\circ}\) and \(30^{\circ}\), respectively. If water enters the impeller radially and velocity of flow remains constant. Determine the work done by the impeller per unit weight of water.