CAIE A-Level Physics 12.2.3 Using a = rω² and a = v²/r

Practise calculating centripetal acceleration with a = r omega² or a = v²/r, rearranging for unknown quantities and choosing consistent units.

Exam points

calculate centripetal acceleration using a = rω² or a = v²/r
rearrange the relationships to determine radius, speed or angular speed
choose the appropriate form and maintain consistent units in a circular-motion calculation

[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 acceleration a of the centre of gravity of the modelling clay.
a= $\mathrm{ms}^{-2}$

$a=v^{2} / r$ or $a=r \omega^{2}$

C1

$\begin{aligned} a =0.68^{2} /(0.093-0.012) \text { or }(0.093-0.012) \times 8.4^{2} =5.7 \mathrm{~m} \mathrm{~s}^{-2} \end{aligned}$

A1

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12.2.3—A = rω2 and a = v2 / r question 1