SECTION 3.7Transmission of Power295Problem 3.7-2A motor drives a shaft at 12 Hz and delivers 20 kW of power (see figure).(a) If the shaft has a diameter of 30 mm, what is the maximum shearstress ±maxin the shaft?(b) If the maximum allowable shear stress is 40 MPa, what is the minimum permissible diameter dminof the shaft?d12 Hz20 kWSolution 3.7-2Motor-driven shaftf²12 HzP²20 kW²20,000 N³m/sTORQUEP²2´fT P²wattsf²Hz²sµ1T²Newton meters(a) MAXIMUM SHEAR STRESSmaxd²30 mmT²P2pf²20,000 W2p(12 Hz)²265.3 N#m (b) MINIMUM DIAMETERdminallow²40 MPa²33.78¶10µ6m3dmin²0.0323 m²32.3 mm;d3²16Tptallow²16(265.3 N#m)p(40 MPa) ²50.0 MPa;tmax²16Tpd3²16(265.3 N#m)p(0.030 m)3Problem 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 maximum
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