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JEE Main 201212 MayOnline
Exam
JEE Main
Year
2012
Date
12 May
Mode
Online
Subject
Physics
Chapter
Laws of Motion

JEE Main 2012 · 12 May · Online · Physics · Laws of Motion

An insect crawls up a hemispherical surface very slowly. The...

An insect crawls up a hemispherical surface very slowly. The coefficient of friction between the insect and the surface is 1/31 / 3. If the line joining the centre of the hemispherical surface to the insect makes an angle α\alpha with the vertical, the maximum possible value of α\alpha so that the insect does not slip is given by An insect crawls up a hemispherical surface very slowly. The coefficient of friction between the insect and the surface

Options

  1. Acot⁡α=3\cot \alpha=3
  2. Bsec⁡α=3\sec \alpha=3
  3. Ccosec⁡α=3\operatorname{cosec} \alpha=3
  4. Dcos⁡α=3\cos \alpha=3

Correct answer

A. cot⁡α=3\cot \alpha=3

Step-by-step solution

An insect crawls up a hemispherical surface very slowly. The coefficient of friction between the insect and the surface
The insect crawls up the bowl upto a certain height hh only till the component of its weight along the bowl is balanced by limiting frictional force. For limiting condition at point AR=mgcos⁡αF1=mgsin⁡α\mathrm{A} R=m g \cos \alpha F_1=m g \sin \alpha Dividing eq. (ii) by (i) tan⁡α=1cot⁡α=F1R=μ[\tan \alpha=\frac{1}{\cot \alpha}=\frac{F_1}{R}=\mu\left[\right. As \left.F_1=\mu R\right] \Rightarrow \quad \tan \alpha=\mu=\frac{1}{3}\left[\because \mu=\frac{1}{3}(\right.Given])∴cot⁡α=3Given \left.]\right) \therefore \quad \cot \alpha=3
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