2. Let the volume of the regular triangular prism $A B C-A^{\prime} B^{\prime} C^{\prime}$ be $V$, and points $P, Q$ lie on edges $A A^{\prime}, C C^{\prime}$ respectively, such that $A P = C^{\prime} Q$. Then the volume of the tetrahedron $B P Q B^{\prime}$ is $\qquad$