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For example: - suppose a body covers a semi-circle in $5$ seconds, then distance$=\pi * r$, where $r$ is the radius of the semi-circle. Displacement is $2r$ only. Then the value of speed is $[\pi * r] / 5$ while that of velocity is $2r/5$. Here we can see that magnitude of velocity is different from that of speed. Is it correct?

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  • $\begingroup$ The displacement is $2r$ and the average velocity is $2r/5$. How do you claim $\pi∗r/5$ is the speed? $\endgroup$ – Mahdi May 6 '17 at 8:03
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Instantaneous speed always equals the magnitude of instantaneous velocity (because the instantaneous displacement is small enough to be regarded as straight-line). In your example, you are comparing average speed and the magnitude of average velocity - and the two of them can be different as you have correctly calculated.

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