Answer: A 0 /9.
- A A<sub>0</sub>/6
- B A<sub>0</sub>/9
- C A<sub>0</sub>/3
- D A<sub>0</sub>/27
Correct answer: B. A<sub>0</sub>/9
Explanation: Amplitude decays as A = A<sub>0</sub>e<sup>-γt</sup>. At 10 s, e<sup>-10γ</sup> = 1/3. At 20 s, e<sup>-20γ</sup> = (1/3)<sup>2</sup> = 1/9, so the amplitude is A<sub>0</sub>/9.
In SHM, displacement and velocity are 90° out of phase (v is maximum when x=0, and zero when x is extreme), while acceleration is always exactly opposite in sign to displacement, consistent with a = −ω²x.
Concept context
Simple harmonic motion, spring-mass, pendulum, energy in SHM, and resonance.