Solution.
Power is calculated by using the formula:
$$
\text { Power }=\frac{\text { Work done }}{\text { Time taken }}
$$
Here, Work done $=20 \mathrm{~J}$
And, Time taken $=5 \mathrm{~s}$
So, putting these values in the above formula, we get:
$$
\begin{aligned}
\text { Power } &=\frac{20 \mathrm{~J}}{5 \mathrm{~s}} \\
&=4 \mathrm{~J} / \mathrm{s} \\
\text { Power } &=4 \mathrm{~W}
\end{aligned}
$$
(because $1 \mathrm{~J} / \mathrm{s}=1 \mathrm{~W}$ )
Thus,the power of this body is 4 watts.