CAIE IGCSE Physics 1.7.1.4 Kinetic energy: Ek = 1/2 mv^2

Practise using Ek = 1/2mv^2 for trolleys, buses, balls, water and moving air, including changes in kinetic energy and power links.

Exam points

substitute mass and speed into Ek = 1/2mv^2 and give the answer in J or kJ
rearrange Ek = 1/2mv^2 to find speed from mass and kinetic energy
use changes in kinetic energy to compare speeds before and after an impact

[Maximum number: 4]

Fig. 2.1 shows a wind turbine.

Fig. 2.1

The wind blows at a speed of $16 \mathrm{~m} / \mathrm{s}$ towards the turbine blades. In one second, a volume of $24000 \mathrm{~m}^{3}$ of air passes through the circular area swept out by the blades. The density of air is $1.3 \mathrm{~kg} / \mathrm{m}^{3}$ .

Calculate:
1. the mass of air that passes through the circular area swept out by the blades in 1.0 s

mass =

2. the kinetic energy of the mass of air that passes through the area swept out by the blades.

kinetic energy =

$1 \mathrm{~d}=\mathrm{m} / \mathrm{V}$ in any form, symbols or words OR $24000 \times 1.3$

C1

31000 kg

A1

$2 \mathrm{KE}=\frac{1}{2} \mathrm{mv}^{2}$ OR $\frac{1}{2} \times 31200 \times 16^{2}$

C1

$4.0 \times 10^{6} \mathrm{~J}$

A1

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1.7.1.4—Kinetic energy: Ek = 1/2 mv^2 question 1