3. An ideal spring is hung vertically from the ceiling. When a 2.0-kg mass hangs at rest from it, the spring is extended 5.0 cm from its relaxed length. A downward external force is now applied to the mass to extend the spring an additional 10 cm. While the spring is being extended by the force, the work done by the spring is about:
(A) -3.92 J
(B)-1.96 J
(C) 0 J
(D) 1.96 J
(E) 3.92 J.
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統計: 尚無統計資料
統計: 尚無統計資料
詳解 (共 2 筆)
#7402681
所以解這題的第一步就是要先判別正負號
彈簧被拉長,彈力向上,恢復力向下
所以作的是負功
利用重力會等於彈力常數乘上伸長量
接著代入變形公式
末狀態平方減掉初狀態平方
一定要是末狀態減掉初狀態
作功公式會等於1/2kx平方
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