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A $0.2 \textrm{ kg}$ mass is being swung round a circle on a light string of length $60 \textrm{ cm}$. It makes $1.4 \textrm{ revolutions per second}$. Find the centripetal force acting on the mass.

My attempt:

enter image description here

Is the final answer correct ?

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  • $\begingroup$ I think a calculator will be of better help than any mathematician! $\endgroup$ – Qwerty Nov 24 '16 at 16:23
  • $\begingroup$ Where did the $77.378$ come from? It seems to have the wrong units, whatever it is. $\endgroup$ – user137731 Nov 24 '16 at 16:23
  • $\begingroup$ That's is true haha but I mean are all the formulas correct ? Such as is w=2 x Pi x f is this correct ? $\endgroup$ – Dan Nov 24 '16 at 16:24
  • $\begingroup$ @Bye_World it came from squaring w. $\endgroup$ – Dan Nov 24 '16 at 16:25
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    $\begingroup$ OK. Then your answer is fine (assuming you multiplied correctly). But the units of $\omega^2$ should be $[s^{-2}]$ (because $\omega$ has units of $[s^{-1}]$). $\endgroup$ – user137731 Nov 24 '16 at 16:26
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The data you have given is:

Frequency($v$)=$1.4$ $Hz$

Mass$=0.2 Kg$

Radius$=0.6m$

Now angular velocity $w$ is given by $2\pi v$ or $w=2\pi v=8.8radians/sec$.

Centripetal force is given by $F_c=mw^2r$ which from the given data is $0.2 * 8.8^2*0.6=9.2928 N$

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