5. (10 points) A water pool has two taps, $A$ and $B$. If $A$ and $B$ are both turned on, it takes 30 minutes to fill the pool. Now, if $A$ and $B$ are both turned on for 10 minutes, and then $A$ is closed, $B$ continues to fill the pool for 40 minutes, the pool can also be filled. If only tap $B$ is turned on to fill the pool, it will take $\qquad$ minutes to fill the pool.
【Analysis】We consider the capacity of the pool as unit "1", first find the work efficiency of pipe $B$, then divide unit "1" by the work efficiency of $B$ to get the time required to fill the pool when only $B$ is opened.

【Solution】Solution: $1 \div\left[\left(1-\frac{1}{30} \times 10\right) \div 40\right]$,
$$
\begin{array}{l}
=1 \div \frac{1}{60}, \\
=60 \text { (minutes); }
\end{array}
$$

Answer: It takes 60 minutes to fill the pool when only the $B$ tap is opened.
Therefore, the answer is: 60.