Work Power and Energy 1 Question 7

8. A uniform chain of length L and mass M is lying on a smooth table and one-third of its length is hanging vertically down over the edge of the table. If g is acceleration due to gravity, the work required to pull the hanging part on to the table is

(1985, 2M)

(a) MgL

(b) MgL/3

(c) MgL/9

(d) MgL/18

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Answer:

Correct Answer: 8. (d)

Solution:

  1. Mass of hanging portion is M/3 (one-third) and centre of mass c, is at a distance h=L6 below the table top. Therefore, the required work done is,

W=mgh=M3(g)L6=MgL18



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