If the rigid body shown is subjected to a general plane motion with respect to the fixed coordinate system x−y, the velocity VA relative to VB (or VA/B) is zero ω×rB/A d(rA/B)/dt always ≠ 0 as long as rA/B ≠ 0.
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If the rigid body shown is subjected to a general plane motion with respect to the fixed coordinate system , the velocity relative to (or ) is
zero
always as long as .