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Rotational Motion question

2019 · 10 Jan · Shift 1 · Q50
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  5. /2019 · 10 Jan · Shift 1 · Q50

Rotational Motion question

2019 · 10 Jan · Shift 1 · Q50

JEE MainPhysicsRotational MotionMCQ+4 / −1
A homogeneous solid cylindrical roller of radius R and mass M is pulled on a cricket pitch by a horizontal force. Assuming rolling without slipping, angular acceleration of the cylinder is -
  1. A
    F2mR{F \over {2mR}}2mRF​
  2. B
    2F3mR{2F \over {3mR}}3mR2F​
  3. C
    3F2mR{3F \over {2mR}}2mR3F​
  4. D
    F3mR{F \over {3mR}}3mRF​
View written solutionFree

Correct answer: B

  1. Given

    • Solid cylinder of mass MMM and radius RRR
    • A horizontal force FFF pulls it
    • Rolling without slipping
  2. Moment of inertia of a solid cylinder about its axis I=12MR2I = \frac{1}{2}MR^2I=21​MR2

  3. Forces acting on the cylinder

    • Applied force FFF at the center, toward the right
    • Static friction fff at the point of contact

    Since the force is applied at the center, it produces no torque about the center. The torque needed for rotation comes from friction.

  4. Translational equation of motion Taking rightward direction as positive: F−f=MaF - f = MaF−f=Ma

  5. Rotational equation about the center Friction provides torque: fR=IαfR = I\alphafR=Iα fR=12MR2αfR = \frac{1}{2}MR^2\alphafR=21​MR2α f=12MRαf = \frac{1}{2}MR\alphaf=21​MRα

  6. Rolling without slipping condition a=αRa = \alpha Ra=αR so α=aR\alpha = \frac{a}{R}α=Ra​

    Substitute into friction expression: f=12MR(aR)=12Maf = \frac{1}{2}MR\left(\frac{a}{R}\right) = \frac{1}{2}Maf=21​MR(Ra​)=21​Ma

  7. Substitute into translational equation F−12Ma=MaF - \frac{1}{2}Ma = MaF−21​Ma=Ma F=32MaF = \frac{3}{2}MaF=23​Ma a=2F3Ma = \frac{2F}{3M}a=3M2F​

  8. Find angular acceleration α=aR=1R⋅2F3M\alpha = \frac{a}{R} = \frac{1}{R}\cdot \frac{2F}{3M}α=Ra​=R1​⋅3M2F​ α=2F3MR\alpha = \frac{2F}{3MR}α=3MR2F​

  9. Match with options α=2F3MR\boxed{\alpha = \frac{2F}{3MR}}α=3MR2F​​ This corresponds to Option B.

  10. Comparison with stored answer Stored correct answer: B

My derived answer also gives B, so they agree.

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