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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Rotational Mechanics

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Rotational Mechanics

A solid sphere and a hollow sphere, both possessing the same mass...

A solid sphere and a hollow sphere, both possessing the same mass and identical radii, are rolled down a rough inclined plane.

Options

  1. AThe solid sphere arrives at the bottom with a greater speed.
  2. BBoth spheres will arrive at the bottom with the same linear momentum.
  3. CThe hollow sphere arrives at the bottom first.
  4. DThe solid sphere arrives at the bottom with a greater kinetic energy.

Correct answer

A. The solid sphere arrives at the bottom with a greater speed.

Step-by-step solution

Let MM be the mass and RR be the radius of both spheres.

The moment of inertia of the solid sphere is IS=25MR2andthatofthehollowsphereisI_S = \dfrac{2}{5}MR^2 and that of the hollow sphere isI_H = \dfrac{2}{3}MR^2.<br><br>Foranobjectrollingdownaninclinedplaneofheight.<br><br>For an object rolling down an inclined plane of heighth,byconservationofmechanicalenergy:<br><br>Mgh=12Mv2+12Iω2, by conservation of mechanical energy:<br><br>Mgh = \dfrac{1}{2}Mv^2 + \dfrac{1}{2}I\omega^2

Since v=ωRv = \omega R for pure rolling:

Mgh = \dfrac{1}{2}Mv^2 \left(1 +\dfrac{I}{MR^2}\right)

v=v =\sqrt{\dfrac{2gh}{1 + \dfrac{I}{MR^2}}}

Since IS<IHI_S < I_H, the denominator is smaller for the solid sphere, giving vS>vHv_S > v_H. Thus, the solid sphere arrives at the bottom with a greater speed.

The acceleration of a rolling body is a=a =\dfrac{g \sin \theta}{1 + \dfrac{I}{MR^2}}. Since IS<IHI_S < I_H, aS>aHa_S > a_H, meaning the solid sphere reaches the bottom first.

Linear momentum is p=Mvp = Mv. Since vS>vHv_S > v_H, pS>pHp_S > p_H.

Total kinetic energy at the bottom is equal to the initial potential energy MghMgh, which is the same for both spheres.
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