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JEE Advanced 2015Paper 1
Exam
JEE Advanced
Year
2015
Paper
Paper 1
Subject
Physics
Chapter
Rotational Motion

JEE Advanced 2015 · Paper 1 · Physics · Rotational Motion

A ring of mass M and radius R is rotating with angular speed ω...

A ring of mass MM and radius RR is rotating with angular speed ω\omega about a fixed vertical axis passing through its centre O with two point masses each of mass M8\dfrac{M}{8} at rest at O. These masses can move radially outwards along two massless rods fixed on the ring as shown in the figure. At some instant the angular speed of the system is 89ω\dfrac{8}{9}\omega and one of the masses is at a distance of 35R\dfrac{3}{5}R from O. At this instant the distance of the other mass from O is

A ring of mass M and radius R is rotating with angular speed ω about a fixed vertical axis passing through its centre O

Options

  1. A23R\dfrac{2}{3}R
  2. B13R\dfrac{1}{3}R
  3. C35R\dfrac{3}{5}R
  4. D45R\dfrac{4}{5}R

Correct answer

D. 45R\dfrac{4}{5}R

Step-by-step solution

Using conservation of angular momentum about axis of ring
MR2ω=MR289ω+M8M{R}^{2}\omega = M{R}^{2}\dfrac{8}{9}\omega + \dfrac{M}{8}\left(\dfrac{9}{25}{R}^{2}\right)(89ω)+Mr28(89ω)\left(\dfrac{8}{9}\omega\right) + \dfrac{M{r}^{2}}{8}\left(\dfrac{8}{9}\omega\right)
r=4R5r = \dfrac{4R}{5}
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