24. A crane lifts a 425 kg steel beam vertically a distance of 117m. How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s2? Neglect frictional forces.
(A) 1.8 x 105 J
(B) 3.4 x 105 J
(C) 4.0 x 105 J
(D) 4.9 x 105 J
(E) 5.8 x 105 J.

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統計： A(1), B(0), C(1), D(1), E(15) #3093865

詳解 (共 1 筆)

#6071872
題目數字設計的不好
照理說是要W = mgh + (1/2)mv2
但mgh = 425*11*9.8 =487300
就剩DE可選了 時間不夠時就會直接選E
ㅤㅤ
由(1/2)at2 =117 算出T～=13 , V～=23.5
(1/2)mv2~=117300
W = mgh + (1/2)mv2加起來最接近E
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