Answer
a. $9.06 \times 10^5 J$
b. $9.06 \times 10^5 J$
c. Yes.
Work Step by Step
a. Find the change in gravitational PE.
$$\Delta PE = mgy_f-mgy_i=mg(y_f-y_i) = (66.5 kg)(9.80 \frac{m}{s^2})(1390 m)=9.06 \times 10^5 J$$
b. This is the minimum work required.
c. The actual work is almost certainly greater than this because the hiker must overcome resistive forces and inefficiencies.
