Question

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

• A. 0.21 cm/s
• B. 1.2 cm/s
• C. 21.0 cm/s
• D. none of these

Answer 1

The correct option is A 0.21 cm/s

Angular speed of second's hand

$\omega =\frac{2\pi }{revolutiontime\left(insec\right)}$

Revolution time of second's hand $=1rev/min=1rev/60sec$

$\Rightarrow \omega =\frac{2\pi }{60sec}$

So the speed of tip of the hand is given by

$\Rightarrow v=r\omega =2cm\times \frac{2\pi }{60sec}\simeq 0.21cm/sec$