CAIE IGCSE Physics Speed as Distance per Unit Time

Practise rearranging v = s/t for speed, distance or time, converting minutes, centimetres and kilometres before applying the equation to motion contexts.

Exam points

choose v = s/t and rearrange it for the unknown distance or time before substituting values
convert minutes to seconds or hours and centimetres or kilometres to the required distance unit
explain direct proportionality of thinking distance to speed when reaction time remains constant

[Maximum number: 3]

Fig. 3.1 shows a model of a wind turbine used to demonstrate the use of wind energy to generate electricity. The wind is blowing towards the model, as shown.

Fig. 3.1

The mass of air passing through the circular area swept out by the turbine blades each second is 7.5 kg . The kinetic energy of the air that passes through this circular area each second is 240 J .

Calculate the speed of the air.

speed =

$\mathrm{KE}=\frac{1}{2} \mathrm{mv}^{2}$ in any form $\mathrm{OR} \mathrm{v}^{2}=2 \times \mathrm{KE} / \mathrm{m}$

OR $240=\frac{1}{2} \times 7.5 \mathrm{v}^{2}$

C1

$v^{2}=2 \times 240 / 7.5 \text { OR }(v=) \sqrt{ }\{2 \times 240 / 7.5\}$ $\mathrm{OR}(\mathrm{v}=) \downarrow\{2 \mathrm{KE} / \mathrm{m}\}$

C1

$=8.0 \mathrm{~m} / \mathrm{s}$

A1

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1.2.1—Speed as distance travelled per unit question 1