Each $0\mathrm{.}55-kg$ ball is attached to the end of the light elastic rod and deflects $4\mathrm{.}7$ mm when a $2\mathrm{.}0-N$ force is statically applied to the ball. If

the central collar is given a vertical harmonic movement with a frequency of $3\mathrm{.}7$ Hz and an amplitude of $4\mathrm{.}0$ mm $,$ find the amplitude $y_0$

of vertical vibration of each ball.