At a waterpark, sleds with riders are sent along a slip-pery, horizontal surface by the release of a large compressed spring. The spring, with force constant k = 40.0 N/cm and negli-gible mass, rests on the frictionless horizontal surface. One end is in contact with a stationary wall. A sled and rider with total mass 70.0 kg arc pushed against the other end, compressing the spring 0.375 m. The sled is then released with zero initial velocity. What is the sled's speed when the spring (a) returns to its uncompressed length and (b) is still compressed 0.200 m?