A mass-spring system oscillates such that the mass  moves on a rough surface having coefficient of
friction $\mu$. It is compressed by a distance a from its normal length and on being released, it moves to a
distance b from its equilibrium position. The decrease in amplitude for one half-cycle (-a to b) is

• A

  $\frac{\mu mg}{k}$

• B

  $\frac{2\mu mg}{k}$

• C

  $\frac{\mu g}{k}$

• D

  $\frac{k}{\mu mg}$