A spring of unstretched length $l$ has a mass $m$ with one end fixed to a rigid support. Assuming spring to be made of a uniform wire, the kinetic energy possessed by it if its free end is pulled with uniform velocity $v$ is:
(1) $\frac{1}{2}mv^{2}$
(2) $mv^{2}$
(3) $\frac{1}{3}mv^{2}$
(4) $\frac{1}{6}mv^{2}$