The length of a spring is 12cm when there is no weight on the lower end, 15cm when there is a 0.6N object on the lower end and the spring is stationary. When there is a 1n weight on the lower end of the spring, the length of the spring is () A. 5 cmB. 17 cmC. 20 cmD. 7 cm

When the object of 0.6N is hung, the spring extends 3cm, so the spring stiffness coefficient is k = FX = 0.6n0.03m = 20n / m. when the weight of 1n is hung at the lower end of the spring, the spring elongation is x '= 120 = 0.05m = 5cm, so the total length of the spring is 17cm

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