A 75-kg roofer climbs a vertical 7.0-m ladder to the flat roof of a house. He then walks 12 m on the roof, climbs down another vertical 7.0-m ladder, and finally walks on the ground back to his starting point. How much work is done on him by gravity?
(a) as he climbs up; (b) as he climbs down;
(c) as he walks on the roof and on the ground?
(d) What is the total work done on him by gravity during this round trip?
(e) On the basis of your answer to part (d), would you say that gravity is a conservative or non-conservative force? Explain.