A Weight Attached to a Spring Starts at Rest $d$ Be the Displacement, in Centimeters, from the Weight's Rest Position

Short Answer

A weight attached to a spring starts at rest. Let $d$ be the displacement, in centimeters, from the weight's rest position. We raise the spring $21 \mathrm{~cm}$ above its rest position and release it at time $t=0$ , where $t$ is in seconds. The weight bobs up and down once every second for a few seconds. The amplitude of the spring's motion shrinks $b$ half every second. Give a model for the spring's motion.