Which of the following statements are true? for the false statements, explain why you think they are false:
(a) feedforward and feedback control require a measured variable.
(b) for feedforward control, the measured variable is the vari able to be controlled.
(c) feedback control theoretically can provide perfect control (i. e., no deviations from set point) if the process model used to design the control system is perfect.
(d) feedback control takes corrective action for all types of process disturbances, both known and unknown.
(e) feedback control is superior to feedforward control.

Tom is having a problem with his washing machine. he notices that the machine vibrates violently at a frequency of 1500 rpm due to an unknown rotating unbalance. the machine is mounted on 4 springs each having a stiffness of 10 kn/m. tom wishes to add an undamped vibration absorber attached by a spring under the machine the machine working frequency ranges between 800 rpm to 2000 rpm and its total mass while loaded is assumed to be 80 kg a) what should be the mass of the absorber added to the machine so that the natural frequency falls outside the working range? b) after a first trial of an absorber using a mass of 35 kg, the amplitude of the oscillation was found to be 10 cm. what is the value of the rotating unbalance? c) using me-3.5 kg.m, find the optimal absorber (by minimizing its mass). what would be the amplitude of the oscillation of the absorber?