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Exercise 3.1 · Q3

Q.A wheel makes 360360 revolutions in one minute. Through how many radians does it turn in one second?

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The wheel's angular speed is found by converting revolutions per minute to radians per second. It turns through 12π12\pi radians in one second.

The key here is understanding what a "revolution" means in angular terms. One full revolution of a wheel corresponds to an angle of 2π2\pi radians — that's the distance around a circle measured in radians, not degrees. So when a wheel spins, every complete turn sweeps out 2π2\pi radians.

The problem gives us a rate: 360 revolutions per minute. But the question asks for the angle turned in one second. So we need to convert from minutes to seconds, and from revolutions to radians, in a clean chain.

Let's work through it step by step.

  1. Find the number of revolutions per second. The wheel makes 360 revolutions in 1 minute. Since 1 minute = 60 seconds, the number of revolutions per second is:

360 revolutions60 seconds=6 revolutions per second.\frac{360 \text{ revolutions}}{60 \text{ seconds}} = 6 \text{ revolutions per second}.

  1. Convert revolutions to radians. Each revolution is 2π2\pi radians. So in one second, the angle turned in radians is:

6 revolutions×2π radians per revolution=12π radians.6 \text{ revolutions} \times 2\pi \text{ radians per revolution} = 12\pi \text{ radians}.

Tip

You can combine both steps into a single calculation:

360 rev1 min×1 min60 s×2π rad1 rev=360×2π60=12π rad/s.\frac{360 \text{ rev}}{1 \text{ min}} \times \frac{1 \text{ min}}{60 \text{ s}} \times \frac{2\pi \text{ rad}}{1 \text{ rev}} = \frac{360 \times 2\pi}{60} = 12\pi \text{ rad/s}.

This gives the angular speed directly — but the question asks for the angle turned in one second, which is numerically the same as the angular speed in rad/s.

Watch out

A common mistake is to forget that one revolution equals 2π2\pi radians, not π\pi radians. Another is to mix up minutes and seconds — always check the time units carefully.

✓Final answer

The wheel turns through 12π\boxed{12\pi} radians in one second.

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