A thick uniform rubber rope of density and Young's modulus
has a length of
When hung from the ceiling of a room, the increase in length of the rope due to its own weight will be
The weight of the rope can be assumed to act at its mid-point. Now, the extension l is proportional to original length L. If the weight of the rope acts at its mid-point, the extension will be that produced by half the rope. So, replacing L by in the expression for Young's modulus, we have
Now therefore