CAIE A-Level Physics Quantity Notation and Unit Interpretation

Practise interpreting prefixes, derived units and dimensions, retaining powers after rearrangement and distinguishing similar symbols from their physical context.

Exam points

use syllabus symbols, prefixes and derived units to express physical quantities correctly
distinguish quantities with similar symbols by interpreting their physical context and dimensions

[Maximum number: 3]

(a)

An isolated planet is a uniform sphere of radius $3.39 \times 10^{6} \mathrm{~m}$ . Its mass of $6.42 \times 10^{23} \mathrm{~kg}$ may be considered to be a point mass concentrated at its centre. The planet rotates about its axis with a period of 24.6 hours.

For an object resting on the surface of the planet at the equator, calculate, to three significant figures:

[ 3 ]

(i)

the centripetal acceleration
acceleration = $\mathrm{ms}^{-2}$

[ 2 ]

$\begin{aligned} a=r \omega^{2} \text { and } \omega=2 \pi / T \text { or } a=v^{2} / r \text { and } v=2 \pi r / T \end{aligned}$

C1

$\begin{aligned} a =3.39 \times 10^{6} \times(2 \pi /(24.6 \times 3600))^{2} =0.0171 \mathrm{~m} \mathrm{~s}^{-2} \end{aligned}$

A1

(ii)

the force per unit mass exerted on the object by the surface of the planet.
force per unit mass = $\mathrm{Nkg}^{-1}$

[ 1 ]

$\begin{aligned} \text { force per unit mass } =3.73-0.0171 =3.71 \mathrm{~N} \mathrm{~kg}^{-1} \end{aligned}$

A1

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Q.2-Quantity notation and unit interpretation in answers question 1

Question (a)

Question (i)

Question (ii)