CAIE A-Level Physics 12.1.3 Using ω = 2π/T and v = rω

Practise relating period, frequency, angular speed, radius and tangential speed in circular motion, using omega = 2pi/T and v = r omega consistently.

Exam points

calculate angular speed using ω = 2π/T and rearrange it to determine period or frequency
calculate linear speed using v = rω and relate radius, angular speed and tangential speed
solve combined circular-motion problems with consistent angular and linear units

[Maximum number: 2]

The metal disc in Fig. 1.1 has a radius of 9.3 cm .

The centre of gravity of the modelling clay is 1.2 cm from the rim of the disc and moves with a speed of $0.68 \mathrm{~ms}^{-1}$ .

Calculate the angular speed $\omega$ of the disc.
$\omega=$ $\mathrm{rad\,s^{-1}}$

$v=r \omega$

C1

$\begin{aligned} \omega =0.68 /(0.093-0.012) =8.4 \mathrm{rad} \mathrm{~s}^{-1} \end{aligned}$

A1

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12.1.3—Ω = 2π / T and v = rω question 1