Chapter 8 - Potential Energy and Conservation of Energy - Problems and Conceptual Exercises - Page 247: 42

$-109J$

We can find $W_{nc_2}$ as follows: $W_{nc}=W_{nc_1}+W_{nc_2}=E_f-E_i=K.E_f-0$ $\implies W_{nc2}=K.E_f-W_{nc_1}$ $W_{nc_2}=\frac{1}{2}mv_f^2-W_{nc_1}$ We plug in the known values to obtain: $W_{nc_2}=\frac{1}{2}(72.0)(1.20)-(161)$ $W_{nc_2}=-109J$