\(\bullet\) \(\bullet\) Food calories. The food calorie, equal to \(4186
\mathrm{J},\) is a
measure of how much energy is released when food is metabo-
lized by the body. A certain brand of fruit-and-cereal bar con-
tains 140 food calories per bar. (a) If a 65 \(\mathrm{kg}\) hiker eats one of
these bars, how high a mountain must he climb to "work off"
the calories, assuming that all the food energy goes only into
increasing gravitational potential energy? (b) If, as is typical,
only 20\(\%\) of the food calories go into mechanical energy, what
would be the answer to part (a)? (Note: In this and all other
problems, we are assuming that 100\(\%\) of the food calories that
are eaten are absorbed and used by the body. This actually
not true. A person's "metabolic efficiency" is the percentage of
calories eaten that are actually used; the rest are eliminated
by the body. Metabolic efficiency varies considerably from
person to person.)