A vertical spring has one end attached to the ceiling and a 2.50-kg fish attached to the other one. When the system is at rest, the spring is stretched by 20.0 cm. Now let the fish drop from a position in which the spring is not deformed at all. Use the conservation of energy law to find:
a) how fast the fish is moving after it drops 20.0 cm;
b) How far down the fish will drop before starting to come back?