A box that has a weight of 40 N is hung from a spring. The spring constant of the spring is 400 N/m.

Use Hooke’s law, F = kx, so the spring’s extension is x = F/k. Substituting the values gives x = 40 N ÷ 400 N/m = 0.1 m, which is 10 cm. The correct choice is 10 cm.

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