Answer
(a)
$$5.184 \times 10^{6} \mathrm{J}$$
---
(b)
Assume that 150 $\mathrm{W}$ is the combined power rating of both lights; then,
$$
\begin{aligned} 864 \times 10^{3} \mathrm{J} \end{aligned}
$$
Work Step by Step
(a)
Energy = Power $\times$ time $=(1 A)(12 V)(120 \mathrm{hr})\left(\frac{60 \mathrm{min}}{\mathrm{hr}}\left(\frac{60 \mathrm{sec}}{\min }\right)\right.$
$\mathrm{w}=5.184 \times 10^{6} \mathrm{J}$
---
(b)
Assume that 150 $\mathrm{W}$ is the combined power rating of both lights; then,
$$
\begin{aligned} \mathbf{W}_{\text {used }}=(150 \mathrm{W})(8 \text { hrs })\left(\frac{3600 \mathrm{sec}}{h r}\right)=4.32 \times 10^{6} \mathrm{J} \\ w_{\text {stored }}=w-w_{\text {used }}=864 \times 10^{3} \mathrm{J} \end{aligned}
$$
