The 20-lb block is attached to a spring having a stiffness of 20 lb/ft. A force F = (6 cos...

The 20-lb block is attached to a spring having a stiffness of 20 lb/ft. A force F = (6 cos 2t) lb, where t is in seconds, is applied to the block. Determine the maximum speed of the block after frictional forces cause the free vibrations to dampen out.