The food calorie, equal to 4186 J, is a measure of how much energy is released when the body metabolizes food. A certain energy bar contains 140 food calories. a) If a 65-kg hiker eats one bar, how high a mountain must he climb to "work off" the calories, assuming that all the food energy goes into increasing gravitational potential energy? b) If, as is more typical, only 20% of the food calories go into mechanical energy, what would the answer be to part (a)?