A helical spring, when fixed at one end and loaded at the other, requires a force of \(100 \mathrm{~N}\) to produce an elongation of \(10 \mathrm{~mm}\). The ends of the spring are now rigidly fixed, one end vertically above the other, and a mass of \(10 \mathrm{~kg}\) is attached at the middle point of its length. Determine the time taken to complete one vibration cycle when the mass is set vibrating in the vertical direction.