LinearVelocity[O,P]

O: name of defined observer

P: name of defined point

The function LinearVelocity returns the linear velocity of the point P relative to the observer O.

Remember to invoke DeclareStates prior to using LinearVelocity.

Restart;
DeclareObservers[A];
DeclarePoints[A,B];
DeclareTriads[a];
DefineObservers[{A,A,a}];
DefinePoints[{A,B,a,q1,q2,q1-q2}];
DeclareStates[q1,q2];
LinearVelocity[A,B]

$\left\{''Type''\to ''Vector'',''Size''\to 1,1\to \left\{''Coordinates''\to \left\{{\mathrm{q1}}^{\prime },{\mathrm{q2}}^{\prime },{\mathrm{q1}}^{\prime }-{\mathrm{q2}}^{\prime }\right\},''Triad''\to a\right\}\right\}$

DeclareStates, AngularVelocity