A block of mass m is attached with a spring of force constant K. Now the other end of the spring is pulled with constant speed u. What is the maximum K.E of the block?$(\mu =0)$

• A

  $\frac{1}{2}m{u}^2$

• B

  $m{u}^2$

• C

  $2m{u}^2$

• D

  $\frac{3}{2}m{u}^2$