(III) A block of mass m is attached to the end of a spring (spring stiffness constant k), Fig. 6-43. The mass is given an initial displacement $x_0$ from equilibrium, and an initial speed $v_0$ .Ignoring friction and the mass of the spring, use energy methods to find ($a$) its maximum speed, and ($b$) its maximum stretch from equilibrium, in terms of the given quantities.