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physics torque 問題求救 !
發問:
FIG 1 :http://session.masteringphysics.com/problemAsset/1260454/2/yf_Figure_10_40.jpgA square metal plate 0.180m on each side is pivoted about an axis through point O at its center and perpendicular to the plate (Figure 1) 問題 : Calculate the net torque about this axis due to the three forces shown in... 顯示更多 FIG 1 : http://session.masteringphysics.com/problemAsset/1260454/2/yf_Figure_10_40.jpg A square metal plate 0.180m on each side is pivoted about an axis through point O at its center and perpendicular to the plate (Figure 1) 問題 : Calculate the net torque about this axis due to the three forces shown in the figure if the magnitudes of the forces are = 28.0 , = 15.8 , and = 15.8 . The plate and all forces are in the plane of the page. Take positive torques to be counterclockwise. 以我理解 : T = F*L T1 = F1*L (28*0.09) 因為 COUNTERCLOCKWISE 所以係正 T2= F2*L (-15.8*0.09) 因為 CLOCKWISE 所以負 T3= F3 COS 45。 * L (15.8COS45。*0.09) 因為 COUNTERCLOCKWISE 所以係正 Tnet= (28*0.09)-15.8*0.09+15.8COS45。*0.09= 2.1 Nm 但係錯左個 ans , 可唔可以 list step 教下我 如果我錯 concept 都 point out t^t 我 physics 好差的 更新: F1=28,F2=15.8,F3=15.8
Torque given by F1 = -28 x 0.09 Nm = -2.52 Nm Torque given by F2 = 15.8 x 0.09 Nm = 1.422 Nm Perpendicular distance of O from F3 = square-root[0.09^2 + 0.09^2] m = 0.1273 m Hence, torque given by F3 = 15.8 x 0.1273 Nm = 2.011 Nm Resultant torque = (-2.52 + 1.422 + 2.011) Nm = 0.913 The direction is counter-clockwise. In your calculation, you have calculated the distance from O to F3 wrongly. Remember that torque = force x perpendicular distance from pivot to force. 2013-03-14 07:38:10 補充： The question gives that "take +ve torque to be counterclockwise", you just adhere to such rule in your calculation here. 2013-03-14 07:48:59 補充： Suppose the corner where force F1 acts be A, say. Then F1 will push the corner A down to the lower right position. Clearly, the square rotates counterclockwise. 2013-03-14 10:18:07 補充： sorry, a typing mistake in the last sentence of the last post. It should be "Clearly, the square rotates clockwise."
其他解答:
唔該晒你呀 好清楚呀 d step, 但係我仲係唔明 d torque 正負點分架,即係點解 f1係負f2同f3係正? 同埋點睇個 torque 係 counter clockwise 定 clockwise? 2013-03-14 19:54:48 補充： okay, i understand now. thank you so much !!!!!!!!!!!! :)) 2013-03-14 19:55:01 補充： thanks so much. i understand now !8758B59A7FA1EEA7
physics torque 問題求救 !
發問:
FIG 1 :http://session.masteringphysics.com/problemAsset/1260454/2/yf_Figure_10_40.jpgA square metal plate 0.180m on each side is pivoted about an axis through point O at its center and perpendicular to the plate (Figure 1) 問題 : Calculate the net torque about this axis due to the three forces shown in... 顯示更多 FIG 1 : http://session.masteringphysics.com/problemAsset/1260454/2/yf_Figure_10_40.jpg A square metal plate 0.180m on each side is pivoted about an axis through point O at its center and perpendicular to the plate (Figure 1) 問題 : Calculate the net torque about this axis due to the three forces shown in the figure if the magnitudes of the forces are = 28.0 , = 15.8 , and = 15.8 . The plate and all forces are in the plane of the page. Take positive torques to be counterclockwise. 以我理解 : T = F*L T1 = F1*L (28*0.09) 因為 COUNTERCLOCKWISE 所以係正 T2= F2*L (-15.8*0.09) 因為 CLOCKWISE 所以負 T3= F3 COS 45。 * L (15.8COS45。*0.09) 因為 COUNTERCLOCKWISE 所以係正 Tnet= (28*0.09)-15.8*0.09+15.8COS45。*0.09= 2.1 Nm 但係錯左個 ans , 可唔可以 list step 教下我 如果我錯 concept 都 point out t^t 我 physics 好差的 更新: F1=28,F2=15.8,F3=15.8
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最佳解答:Torque given by F1 = -28 x 0.09 Nm = -2.52 Nm Torque given by F2 = 15.8 x 0.09 Nm = 1.422 Nm Perpendicular distance of O from F3 = square-root[0.09^2 + 0.09^2] m = 0.1273 m Hence, torque given by F3 = 15.8 x 0.1273 Nm = 2.011 Nm Resultant torque = (-2.52 + 1.422 + 2.011) Nm = 0.913 The direction is counter-clockwise. In your calculation, you have calculated the distance from O to F3 wrongly. Remember that torque = force x perpendicular distance from pivot to force. 2013-03-14 07:38:10 補充： The question gives that "take +ve torque to be counterclockwise", you just adhere to such rule in your calculation here. 2013-03-14 07:48:59 補充： Suppose the corner where force F1 acts be A, say. Then F1 will push the corner A down to the lower right position. Clearly, the square rotates counterclockwise. 2013-03-14 10:18:07 補充： sorry, a typing mistake in the last sentence of the last post. It should be "Clearly, the square rotates clockwise."
其他解答:
唔該晒你呀 好清楚呀 d step, 但係我仲係唔明 d torque 正負點分架,即係點解 f1係負f2同f3係正? 同埋點睇個 torque 係 counter clockwise 定 clockwise? 2013-03-14 19:54:48 補充： okay, i understand now. thank you so much !!!!!!!!!!!! :)) 2013-03-14 19:55:01 補充： thanks so much. i understand now !8758B59A7FA1EEA7
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