4. (15 points) A free vibration of the mechanical system shown in Figure 3 (not to scale) indicates that the amplitude of vibration decreased from x = 4 at t=t to x5 = 0.2 at t = ts after four consecutive cycles. Determine the corresponding viscous friction coefficient b if m = 20 kg and k 500 N/m in the system. Figure 3 17 1-(8) www Est Figure 4 -Constant Gear 1 Gear 2