Question

There are two points P and Q on a planar rigid body. The relative velocity between the two points

(a) should always be along PQ

(b) can be oriented along any direction

(c) should always be perpendicular to PQ

(d) should be along QP when the body undergoes pure translation

The question was asked in quiz.

I want to ask this question from Velocity of a point Link on a Link By Instanteneous Centre Method topic in division Velocity in Mechanisms of Machine Kinematics

Answer 1

The correct choice is (c) should always be perpendicular to PQ

Best explanation: Velocity of any point on a link with respect to another point (relative velocity) on the same link is always perpendicular to the line joining these points on the configuration (or space) diagram.

vQP = Relative velocity between P & Q

               = vP − vQ always perpendicular to PQ.