Damped Harmonic Motion: a Lightly Damped Harmonic Oscillator, with a Damping

Multiple Choice

Damped harmonic motion: A lightly damped harmonic oscillator, with a damping force proportional to its speed, is oscillating with an amplitude of 0.500 cm at time t = 0. When t = 8.20 s, the amplitude has died down to 0.400 cm. At what value of t will the oscillations have an amplitude of 0.250 cm?

A) 18.5 s
B) 20.5 s
C) 16.5 s
D) 25.5 s
E) 5.13 s