Con lắc đơn gồm vật nhỏ khối lượng 200g, dây treo có chiều dài l = 1,2m. Kéo vật ra khỏi vị trí cân bằng sao cho dây treo hợp với phương thẳng đứng góc 60o rồi thả nhẹ. Lấy g = 10m/s2. Chọn gốc thế năng tại vị trí cân bằng. Cơ năng của vật tại vị trí thả vật là: * 1 điểm 2,4 J 0,5 J 2 J 1,2 J làm giúp mình vs ạ, mình cảm ơn

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