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Question
A ladder AB, 2.5 m long and of weight 150 N has its centre of gravity 1 m from A is lying flat on ground. A weight of 40 N is attached to the end B. The work required (in joule) to raise the ladder from the horizontal position to vertical position so that the bottom end A is resting in a ditch 1 m below the ground level will be :
A ladder AB, 2.5 m long and of weight 150 N has its centre of gravity 1 m from A is lying flat on ground. A weight of 40 N is attached to the end B. The work required (in joule) to raise the ladder from the horizontal position to vertical position so that the bottom end A is resting in a ditch 1 m below the ground level will be :
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Solution
The correct option is A 60
Work done is increase the potential energy in
(i) Moving the weight of 150N of the ladder. Since the vertical position of center of mass of the ladder is 1m from A, its final position is also at ground and hence, no change in potential energy occurs.
(ii) Moving the weight 40N attached at the end of the ladder. As the ladder is moved to the new position, the 40N weight moves 1.5m above the ground and hence, the change in potential energy is 40×1.5J.Work done is given by:
W=0+40×1.5
W=60J
Work done is increase the potential energy in
(i) Moving the weight of 150N of the ladder. Since the vertical position of center of mass of the ladder is 1m from A, its final position is also at ground and hence, no change in potential energy occurs.
(ii) Moving the weight 40N attached at the end of the ladder. As the ladder is moved to the new position, the 40N weight moves 1.5m above the ground and hence, the change in potential energy is 40×1.5J.
Work done is given by:
W=0+40×1.5
W=60J
W=0+40×1.5
W=60J
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