physics - energy

2010-05-09 4:22 am

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更新1:

http://i409.photobucket.com/albums/pp172/momoko_deedee/phy_A5.jpg 唔洗理上面果2條LINK* 洗係LEE個就OK...THX^^

更新2:

淨係*****

回答 (1)

天同

2010-05-09 8:58 am

✔ 最佳答案

(A) The angle (theta) at which the rope makes with the vertical when the bag is displaced = arc-sin(2.2/3.7) degrees = 36.48 degrees
Hence, let T be the tension in the rope,
T.cos(theta) = 110g
where g is the acceleration due to gravity (= 9.81 m/s2)
i.e. T = 110g/cos(theta)
The required horizontal force = T.sin(theta) = [110g/cos(theta)].sin(theta)
= 110g.tan(theta) = 110 x 9.81 x tan(36.48) N = 798 N

(B) work done by the rope = 0 J

(C) Work done by worker = increase in potential energy of the bag
= 110g x [3.7 - 3.7.cos(36.48)] J = 782 J

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