Chapter 18 - Exercises and Problems - Page 330: 19

$-14 kW$

First, we find $dQ/dt$: $ \frac{dQ}{dt} = \frac{dU}{dt} - \frac{dW}{dt} = 100 - 17 = 83$ Thus, the total energy is only 68/83 = 82% of the original energy. Since 17 percent of the energy is mechanical, we multiply: $.82 \times 17 = 14$ kW Since energy is released, we know this value is actually $-14 kW$.