A damped harmonic oscillator consists of a block (m = 2.00 kg), a spring (k = 10.0 N/m), and a damping force the is linearly proportional to the velocity. Initially, it oscillates with an amplitude of 25.0 cm; because of damping, the amplitude falls to three-forths of this initial value at the completion of four oscillations. (a) What is the value of time constant ?? (b) How much energy has been "lost" during these four oscillations?