Instantaneous axis of rotation and other ways to find velocity of points on a moving triangle.

00:29 Hints given | 02:54 First solution | 06:31 Second solution | 08:40 Third solution | 12:07 Answer

Question R4L2: Concepts used in solution

Instantaneous axis of rotation | Relative velocity |  Velocity due to rotation

Instantaneous axis of rotation explained in MIT OCW

Definition and simulation in 3D available here

Problem statement

A, B, and C are vertices of a moving rigid equilateral triangle. At a particular instant, A moves with velocity u along AB towards B. C moves away from B along BC with an unknown speed. Find the velocity of B.