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:
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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:

G1 Physics · Accepted Answer

Step 1: The wire extends from L to L + l, so the extension is ΔL = l. Step 2: When the suspended block is in equilibrium, the final tension is F = Mg. Step 3: For elastic loading obeying Hooke's law, force rises linearly from 0 to Mg as the extension increases from 0 to l. Step 4: Stored elastic energy is the area under the F–ΔL graph: U = ½FΔL. Step 5: U = ½Mgl. Final answer: (B) ½Mgl.