Math CentralQuandaries & Queries


Question from Julia:

A wheel of a child’s car revolves at 10 rpm. A painted dot on the circumference of the wheel is 12 cm from the centre of rotation of the wheel. How far does the dot travel in 5 s, to one decimal place?

Hi Julia,

You have time measured in minutes in one place and seconds in another. Let's measure time in seconds in both. Since thee are 60 seconds in a minute the wheel rotates at $\large \frac{10}{60} \normalsize = \large \frac{1}{6}$ revolutions per second. Hence in 5 seconds the dot on the wheel will travel $\large \frac56$ of a revolution. One revolution of the dot is the circumference of a circle of radius 12 cm.


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