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BITSAT 2020 Paper

Section: Physics

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Question : 3 of 150

Marks: +1, -0

The upper half of an inclined plane with inclination

\phi

is perfectly smooth while the lower half is rough. A body starting from rest at the top will again come to rest at the bottom if the coefficient of friction for the lower half is given by

$2 \cos \phi$
$2 \sin \phi$
$\tan \phi$
$2 \tan \phi$

Solution:

Acceleration of block while sliding down upper half

=g \sin \phi

retardation of block while sliding down lower half

=-(g \sin \phi-\mu g \cos \phi)

For the block to come to rest at the bottom, acceleration in I half = retardation in II half.

g \sin \phi=-(g \sin \phi-\mu g \cos \phi)

\Rightarrow \mu=2 \tan \phi

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