**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.**