A quick return mechanism is shown in below. The crank OS is drive at $$2$$ rev/s in counter clockwise direction

The angular speed of PQ in rev/s when the block R attains maximum speed during forward stroke (stroke with slower speed) is

Match the items in column $$I$$ and $$II$$

List $$I$$
$$P.$$ Higher kinematic pair
$$Q.$$ Lower kinematic pair
$$R.$$ Quick return mechanism
$$S.$$ Mobility of a linkage

List $$II$$
$$1.$$ Grubler's equation
$$2.$$ Line contact
$$3.$$ Euler's equation
$$4.$$ planar
$$5.$$ Shaper
$$6.$$ Surface contact

In a four-bar linkage, $$S$$ denotes the shortest link length, $$L$$ is the longest link length, $$P$$ and $$Q$$ are the lengths of other two links. At least one of the three moving links will rotate by $${360^ \circ }$$ if

An instantaneous configuration of a four-bar mechanism, whose plane is horizontal, is shown in the figure below. At this instant, the angular velocity and angular acceleration of link $${Q_2}\,\,A$$ are $$\omega = 8\,\,rad/s$$ and $$\alpha = 0$$, respectively, and the driving torque $$(T)$$ is zero. The link $${Q_2}\,\,A$$ is balanced so that its center of mass falls at $${Q_2}.$$

At the instant considered, what is the magnitude of the angular velocity of $${O_4}B?$$