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lethihong3
2 năm trước
Câu 4. (1đ). Chú Bình muốn nâng hòn đá nặng 60 kg lên cao. Hỏi a) Nếu chú Bình sử dụng ròng rọc cố định phải dùng một lực kéo là bao nhiêu? b) Nếu chú Bình sử dụng pa lăng gồm 3 ròng rọc cố định và 3ròng rọc động thì phải dùng một lực kéo là bao nhiêu?
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