Một lò xo nhẹ có các vòng giống hệt nhau đc treo thẳng đứng . lần lượt buộc vật nặng vào đầu dưới và vào điểm giữa của lò xo thì khi vật đứng cân bằng , độ giãn của lò xo ứng vs là denta L1 và denta L2 .Biết độ cứng của lò xo tỉ lệ nghịch vs chiều dài tự nhiên của .Tỉ số denta L1 / denta L2

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