A pulley used to transmit power by means of ropes has a diameter of \(3.6 \mathrm{~m}\) and has 15 grooves of \(45^{\circ}\) angle. The angle of contact is \(170^{\circ}\) and coefficient of friction between ropes and groove side is 0.28 . The maximum possible tension in the ropes is \(960 \mathrm{~N}\) and rope mass is \(1.5 \mathrm{~kg}\) per metre length. Calculate the pulley speed in rpm and maximum power transmitted.