(1)
弹簧不挂物体时的长度为 y0,
y0 = 12 cm
(2)
因为 x = 2(y - 12)
所以 y = x/2 + 12 ,0 ≤ x ≤ 25
(3)
x = 14 kg 时,
y = x/2 + 12
= 19 cm