An elevator of mass m is initially at rest on the first floor of a building. it moves upward, and passes the second and third floors with a constant velocity, and finally stops at the fourth floor. the distance between adjacent floors is h. what is the net work done on the elevator during the entire trip, from the first floor to the fourth floor?
1. w = ? 4 m g h
2. none of these.
3. w = 0
4. w = 4 m g h
5. w = ? 3 m g h
6. w = 3 m g h