13. A block of mass m = 2 kg is placed on a horizontal frictionless surface. A spring (spring constant of 800 N/m) is attached to the wall. The block is pushed to compress the spring by 0.1 m and a cord initially holds the block in place (the top figure). The chord is cut and the block is released to move freely on the surface (the lower figure). (a) (5 pts) What is the potential energy stored in the spring when it is compressed? Before After -1.8 m-- (b) (5 pts) What is the lock's speed when it leaves contact with the spring? c) (5 points) As the block moves to the right, it encounters a rough section of the surface and comes to ween the block a