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JEE Main 2014 (12 Apr, Shift 1) · Angular Momentum & its Conservation

Angular Momentum & its Conservation question from JEE Main 2014 (12 Apr, Shift 1)

Q75JEE Main 2014 · 12 APR · SHIFT 1Medium

Angular Momentum & its Conservation

A particle is moving in a circular path of radius a, with a constant velocity vv as shown in the figure. The center of circle is marked by 'C'. The angular momentum from the origin O can be written as:

Figure

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Answer: (a)

OCPθ2θa
  1. Angle at the centre is twice the angle at the circumference, so CP makes 2θ2\theta with the x-axis.
  2. P=(a+acos⁡2θ, asin⁡2θ)P=(a+a\cos2\theta,\ a\sin2\theta); tangential velocity v⃗=v(−sin⁡2θ, cos⁡2θ)\vec v=v(-\sin2\theta,\ \cos2\theta).
  3. L/m=xvy−yvx=va[(1+cos⁡2θ)cos⁡2θ+sin⁡22θ]L/m=xv_y-yv_x=va[(1+\cos2\theta)\cos2\theta+\sin^2 2\theta]
  4. L/m=va(1+cos⁡2θ)L/m=va(1+\cos2\theta) (options are written per unit mass).
  5. So the answer is (a) va(1+cos⁡2θ)va(1+\cos2\theta).
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