Natural length of a massless spring (of spring constant k) is x. It is slowly stretched by applying an external force. What is the work done in slowly increasing its extension from 3x to 4x?
A
1.5kx2
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B
2.5kx2
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C
−3.5kx2
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D
3.5kx2
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Solution
The correct option is D3.5kx2 It is given in the problem that, Initial displacement =3x and Final displacement =4x So, work done by external force is given by W=12(kx2f−kx2i) W=12kx2(16−9) W=3.5kx2 Therefore, work done by the external force is, W=3.5kx2