A wheel of radius 1 meter rolls forward ha

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A wheel of radius $1$ meter rolls forward half a revolution on a horizontal ground. The magnitude of the displacement of the point of the wheel initially in contact with the ground is

A

$2\pi $

B

$\sqrt 2 \pi $

C

$\sqrt {{\pi ^2} + 4} $

D

$\pi$

A wheel of radius $1$ meter rolls forward half a revolution on a horizontal ground. The magnitude of the displacement of the point of the wheel initially in contact with the ground is

Horizontal distance covered by the wheel in half revolution = $\pi R.$

So the displacement of the point which was initially in contact with ground $= AA'$ $ = \sqrt {{{(\pi R)}^2} + {{(2R)}^2}} $

$=R\sqrt {{\pi ^2} + 4} $ $ = \sqrt {{\pi ^2} + 4} $    $(As\,R = 1m)$