A rigid rod of length $1 \: m$ is resting at an angle $\theta =45^{\circ}$ as shown in the figure. The end $P$ is dragged with a velocity of $U=5 \: m/s$ to the right. At the instant shown, the magnitude of the velocity $V$ (in $m/s$) of point $Q$ as it moves along the wall without losing contact is
- $5$
- $6$
- $8$
- $10$