For a CSTR with a flow rate equal to 1,000 m3/day, an influent contaminant concentration (C0) equal to 200 mg/L and a second-order reaction rate constant (k) equal to 0.2 L/mg-day, calculate the steady-state hydraulic retention time (t0, days) and the reactor volume (V, m3) necessary to achieve a contaminant removal efficiency equal to 90%.

Aloaded platform of total mass 500 kg is supported by a dashpot and by a set of springs of effective stiffness 72 kn/m. it is observed that when the platform is depressed through a distance x = 12.5 cm below its equilibrium position and then released without any initial velocity; it reaches its equilibrium position in the shortest possible time without overshoot. find the position and velocity of the loaded platform 0.10 sec. after its release. if a further load of 400 kg is added to the platform, find, i) the frequency of damped vibrations, and i) the amplitude of vibration after 2 complete oscillations, given that the initial amplitude is 15 cm.