A vehicle suspension system consists of a spring and a damper. The stiffness of the spring is 3.6 kN/m and the damping constant of the damper is 400 Ns/m. If the mass is 50 kg, then the damping factor (d ) and damped natural frequency (fn), respectively, are

• A. 0.471 and 1.19 Hz
• B. 0.471 and 7.48 Hz
• C. 0.666 and 1.35 Hz
• D. 0.666 and 8.50 Hz