Chapter 10 - Interactions and Potential Energy - Exercises and Problems - Page 255: 2

(a) $W_{int} = 5~J$ (b) $W_{ext} = 2~J$

(a) We can find $W_{int}$: $W_{int} = -\Delta U_{int}$ $W_{int} = -(-5~J)$ $W_{int} = 5~J$ (b) We can find $W_{ext}$: $W_{ext} = \Delta K+\Delta U_{int}$ $W_{ext} = (7~J)+(-5~J)$ $W_{ext} = 2~J$