Problem 3.7-2A motor drives a shaft at 12 Hz and delivers 20 kW ofpower (see figure). (a) If the shaft has a diameter of 30 mm, what is the maximum shearstress tmaxin the shaft? (b) If the maximum allowable shear stress is 40 MPa, what is theminimum permissible diameter dminof the shaft?Solution 3.7-2Motor-driven shaftSECTION 3.7Transmission of Power217d12 Hz20 kWf512 HzP520 kW520,000 N ? m/sTORQUEP52pfT P5wattsf5Hz5s21T5Newton meters(a) MAXIMUM SHEAR STRESStmaxd530 mmT5P2pf520,000W2p(12Hz)5265.3N .m(b) MINIMUM DIAMETERdmintallow540 MPadmin50.0323m532.3mmÊ533.7831026m3d3516Tptallow516(265.3N .m)p(40MPa)550.0MPaÊtmax516Tpd3516(265.3N .p(0.0303Problem 3.7-3The propeller shaft of a large ship has outside diameter 18 in. and inside diameter 12 in., as shown in the figure. The shaft is rated for a maximum shear stress of 4500 psi. (a) If the shaft is turning at 100 rpm, what is the maximumhorsepower that can be transmitted without exceeding theallowable stress?
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