two $400$mm diameter pulleys are keyed to a simply supported shaft $500$mm apart.each pulley is $100$mm from its support and has horizontal belts $,$tension ratio being $2\mathrm{.}5.$if the shear stress is to be limited to $80$MPa while transmitting $45$kW at $900$ rpm$.$find the shaft diameter if it is to be used for the input$-$output belts being on the same or opposite sides