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

1. $5$
2. $6$
3. $8$
4. $10$