CAIE A-Level Physics Quantities, Symbols and Units

Practise using CAIE A-Level Physics units and quantity notation to define derived units, label calculated values and interpret physical meaning from context.

Exam points

use physical symbols, prefixes and derived units accurately in calculations
distinguish similar symbols and dimensions by interpreting the physical quantity and context

Covered syllabus points

Q.1-Base quantities, symbols and SI units Q.2-Quantity notation and unit interpretation in answers

[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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Covered syllabus points

Key quantities, symbols and units question 1

Question (a)

Question (i)

Question (ii)