Let L be length of string.The work done in displacing the mass is given by FLsin 45. This work is stored as gravitational potential energy. The mass rises from a length L to Lcos45. Draw the diagram and u will know that.Hence change in gravitational potential energy is Mg (L- L cos 45). Using work- energy theorem,
FLsin 45 = Mg (L - L cos 45)
F= MG(1-cos45)/sin45
F = Mg (
2 - 1)
Hence 1st choice is correct.
Moderation Team
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