An "energy bar" contains 22g of carbohydrates. If the energy bar was his only fuel, how far could a 68 kg person walk at 5 km/hr ?

Answer 1

According to
http://walking.about.com/library/cal/uccalc1.htm ,
about 80 Calories are burned per mile for a person of that weight, walking at that speed. That amounts to 50 Calories per km. 22g of carbohydrates contain 88 Calories. That means a person can walk 88/50 = 1.8 km while burning the Calpries in that energy bar.

Of course, a person can walk farther than that by using energy stored in the body as fat or residual blood sugar. That is one way to diet.