The second's hand of a watch is 2cm long, the speed of the tip of this hand is 

A. 0.21 cm/s  B. 2.1 cm/s C. 21.0 cm/s

I think we can solve this question by calculating angular velocity.

The circular path of the tip of the watch is, d = 2 × π  × r = 2 × 3.14 × 2 = 12.56 cm

The time in which the tip covers one revolution, t = 60 s

So,

The speed of the tip is,v = 12.56/60 = 0.21 cm/s

Correct option is A.

Yes, you can calculate the same by first finding the angular velocity.

Angular velocity, ω = 2π/t (t = 60 s)

Speed, v = rω = 2πr/t

Which again gives us the same result.

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