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 nonconservative force? Explain.

Solution 28E The equation for work done by gravity is given by W = mgh, where is the mass of the body, g is the acceleration due to gravity and h is the height. The situation asked in the question can be understood from the figure shown below. The roofer starts at A and then reaches the same point after climbing and walking through the paths as shown. Given, mass of the roofer m = 75 kg h = 7.0 m (a) As he climb up against gravity, the acceleration due to gravity is g = 9.80 m/s Therefore, work done on him by gravity as he climbs up is W = 75 kg × ( 9.80 m/s ) × 7.0 m = 5145 J 1 (b) Work done on him as he climbs down the ladder is W 2 = 75 kg × 9.80 m/s × 7.0 m = 5145 J (c) As he walks on the ground,...