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I am totally confused on how to calculate this. The whole entire question is: A hour hand is 20cm long. The speed of the hour hand tip is ________m/s. No other info other than that. Anyone help?

NathanTGM
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    Hint: If you know the angular velocity $\omega$ and the radius $r$, the speed is $r\omega$. Alternatively, just work out the distance travelled by the hour hand in some known amount of time, then use $speed = distance/time$. – Minus One-Twelfth May 22 '19 at 09:20
  • Remember you can accept an answer using the green tick by the answer you would like to choose! –  May 22 '19 at 12:58

2 Answers2

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This is just circular motion its easier than you think! For something moving in a circle the speed at any radius $r$ is given by $v=\frac{2\pi r}{t}$. So $20$cm in meters is $0.2$ and the time for it do to one revolution is $3600\times12$ seconds as it takes $12$ hours for one full revolution and that takes $12$ hours or $43200$ seconds!

So $v=\frac{2\pi \times 0.2}{3600\times 12}$

Roughly $0.00003$ meters per second!

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You can calculate exactly what the disatance the tip travels in 12 hours (hint: it travels the whole circle).

The speed is simply distance (which you can calculate) divided by time (which you know is 12 hours).

5xum
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