Q-30) A ring of radius R is rolling without slipping over rough horizontal surface with velocity v0. Two points are located at A and B on rim of ring. Find angular velocity of A w.r.t. B.


1   v 0 R 2   2 v 0 R 3   2 v 0 R 4   v 0 2 R



vP=vQ+ω×rPQ, where P and Q are general point on rigid body and rPQ is position vector of P with respect to QChoose P=A and Q=CvA=vC+ω×rACGivenvC=v0 i^rAC=Rj^ω=ωk^By condition of no slipping, ω=v0R ω=-v0R k^ body is rolling clockwise so direction of angular velocity will be along -z axisThereforevA=v0i^-v0Rk^×Rj^vA=v0i^-v0RRk^×j^vA=v0i^+v0i^vA=2v0i^SimilarlyvB=vC+ω×rBCrBC=Ri^vB=v0i^-v0Rk^×Ri^vB=v0i^-v0RRk^×i^vB=v0i^-v0j^Now we know, let angular velocity of A with respect to B be ω'ω'=ω'k^vA=vB+ω'×rABrAB=-Ri^+Rj^2v0i^=v0i^-v0j^+ω'k^×-Ri^+Rj^2v0i^=v0i^-v0j^+ω'Rk^×-i^+ω'Rk^×j^2v0i^=v0i^-v0j^-ω'Rj^-ω'Ri^v0i^+v0j^=-ω'Rj^-ω'Ri^Clearly we have-ω'Rj^=v0ω'=-v0Rω '=-v0Rk^
You can take is as a general result that angular velocity of any point of the body with respect to any other point is same and equal to angular velocity of the body. 

  • 9
Is the answer 2?
  • -6
Angular velocity will be uniform throughout the ring because the axis of rotation rotates with a particular speed. The angular velocity at b is towards -j that is downward and that at a is towards +i that is forward. So we know the relative velocity relation. So angular velocity of a wrt b is v/r i -(- v/r j) Which is v/r i+ v/r j. The mod is option b.
  • -5
What are you looking for?