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18 tháng 6 2020

 có 2 loại ròng rọc 

ròng rọc cố định giúp làm thay đổi   của lực kéo so với khi kéo trực tiếp

ròng rọc động giúp làm lực kéo vật lên nhỏ hưn tronhgj lượng của vật

dùng palăng cho phép giảm giảm cường độ lực kéo

21 tháng 6 2020

mày ko thoát dược đâu con trai to be 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mà thôi