9. A mass weighing 8 pounds is attached to a spring. When set in motion, the spring/mass system exhibits simple harmonic motion. (a) Determine the equation of motion if the spring con- stant is 1 1b/ft and the mass is initially released from a point 6 inches below the equilibrium position with a downward velocity of = fi/s. (b) Express the equation of motion in the form given in (6). (c) Express the equation of motion in the form given in (6')