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Rotational Motion question

2005 · Shift 0 · Q177
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  5. /2005 · Shift 0 · Q177

Rotational Motion question

2005 · Shift 0 · Q177

JEE MainPhysicsRotational MotionMCQ+4 / −1
An annular ring with inner and outer radii R1{R_1}R1​ and R2{R_2}R2​ is rolling without slipping with a uniform angular speed. The ratio of the forces experienced by the two particles situated on the inner and outer parts of the ring, F1F2 {{{F_1}} \over {{F_2}}}\,F2​F1​​ is
  1. A
    (R1R2)2{\left( {{{{R_1}} \over {{R_2}}}} \right)^2}(R2​R1​​)2
  2. B
    R2R1{{{{R_2}} \over {{R_1}}}}R1​R2​​
  3. C
    R1R2{{{{R_1}} \over {{R_2}}}}R2​R1​​
  4. D
    111
View written solutionFree

Correct answer: C

  1. Interpret the situation

An annular ring is rolling without slipping with uniform angular speed ω\omegaω.

We need the ratio of the forces experienced by:

  • a particle on the inner circle of radius R1R_1R1​
  • a particle on the outer circle of radius R2R_2R2​

Since the ring is rotating with uniform angular speed, each particle moves in a circle about the center of the ring.

So the required force is the centripetal force:

F=mω2rF = m\omega^2 rF=mω2r

where rrr is the distance of the particle from the center.


  1. Force on particle at inner radius R1R_1R1​

If the mass of each particle is mmm, then

F1=mω2R1F_1 = m\omega^2 R_1F1​=mω2R1​


  1. Force on particle at outer radius R2R_2R2​

Similarly,

F2=mω2R2F_2 = m\omega^2 R_2F2​=mω2R2​


  1. Take the ratio

F1F2=mω2R1mω2R2=R1R2\frac{F_1}{F_2} = \frac{m\omega^2 R_1}{m\omega^2 R_2} = \frac{R_1}{R_2}F2​F1​​=mω2R2​mω2R1​​=R2​R1​​


  1. Match with options

F1F2=R1R2\frac{F_1}{F_2} = \frac{R_1}{R_2}F2​F1​​=R2​R1​​

So the correct option is:

C. R1R2\displaystyle \frac{R_1}{R_2}R2​R1​​


  1. Comparison with stored correct answer

Stored correct answer: C

Our derived answer: C

They match.

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