E = ½KA^2 is the mechanical energy of any oscillator. It is the sum of elastic potential energy and kinetic energy. When amplitude A decreases by 3%, then
(E2-E1)/E1 = {½K(A2^2/A1^2) }/ ½K(A1^2)
= {(A2^2 – A1^2) / (A1^2)}
= 97^2 – 100^2/100^2
= 5.91% of the mechanical energy is lost each cycle.