The second's hand of a watch is $2 c m$ long. The speed of the tip of this hand is:

0.21 c m / s

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2.1 c m / s

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21.0 c m / s

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None of these

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Solution

The correct option is B $0.21 c m / s$
Given : Radius, $r = 2 c m$ (length of seconds hand)
The second's hand completes its one round in $60 s$ .
$∴$ Speed $= \frac{2 π r}{t i m e} = 2 \times \frac{22}{7} \times \frac{2}{60} = 0.21 c m / s$

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