Chapter 10 - Interactions and Potential Energy - Conceptual Questions - Page 255: 12

$W_{ext} = 0$ $U_{Gf} = 0$ $K_f = 2~J$

Since there is no force acting on the firefighter except for the gravitational force and the frictional force which is accounted for in $\Delta E_{th}$, then $W_{ext} = 0$ Since the firefighter is on the ground at the end, $U_{Gf} = 0$ Since energy must be conserved, $K_f = 2~J$