Câu hỏi

Để xiết chặt một êcu, người ta tác dụng lên một đầu cán cờ lê một lực làm với cán cờ lê một góc α (Hình 3.6). a) Xác định dấu của momen lực F → " src="data:image/jpeg;charset=utf-8;base64,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" style="width: 9.33px; height: 16.00px; margin-left: 0.00px; margin-top: 0.00px; transform: rotate(0.00rad) translateZ(0px); -webkit-transform: rotate(0.00rad) translateZ(0px);" title="F with rightwards arrow on top"> đối với trục quay của êcu. b) Viết biểu thức của momen lực F → " src="data:image/jpeg;charset=utf-8;base64,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" style="width: 9.33px; height: 16.00px; margin-left: 0.00px; margin-top: 0.00px; transform: rotate(0.00rad) translateZ(0px); -webkit-transform: rotate(0.00rad) translateZ(0px);" title="F with rightwards arrow on top"> đối với trục của êcu. c) Tính momen đó, biết F = 20N; OA = 0,15m và α = 60 ° " src="data:image/jpeg;charset=utf-8;base64,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" style="width: 48.00px; height: 10.67px; margin-left: 0.00px; margin-top: 0.00px; transform: rotate(0.00rad) translateZ(0px); -webkit-transform: rotate(0.00rad) translateZ(0px);" title="alpha equals 60 degree"> .