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When a block of mass M is suspended by a long wire of length L, the length of the wire becomes (L + l). The elastic potential energy stored in the extended wire is :
(3) 12Mgl
In equilibrium the stretching force on the wire is F = Mg and the extension is l.
As per NCERT, elastic potential energy stored in a stretched wire:
U = 12 stress strain volume = 12F l
∴ U = 12Mgl
Answer: (3)
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