Cambridge International Mathematics

EXERCISE 30A.1

1 h^012345

W 0 12 : 50 25 : 00 37 : 50 50 : 00 62 : 50

The table alongside shows the total wages

$Wearned for workinghhours.

a Draw a graph ofWagainsth.

b AreWandhdirectly proportional? Explain your answer using the features of your graph.

c IfW andhare directly proportional, determine:

i the proportionality constant ii the law connectingW andh.

2 Ifyis directly proportional tox, state what happens to:

a yifxis doubled b yifxis trebled

c xifyis doubled d xifyis halved

e yifxis increased by20% f xifyis decreased by30%

g yif 2 is added tox h yif 3 is subtracted fromx:

3 Which of the following graphs indicate thatyis directly proportional tox?

abcd

4 The law connecting the circumferenceCand radiusrof a circle is C=2¼r.

a Explain why C/r.

b Find the proportionality constant.

c What happens to: i Cifris doubled ii rifCis increased by50%?

5 If y/x and y= 123 when x=7: 1 , find:

a y when x=13: 2 b x when y= 391.

6 The resistanceRohms to the flow of electricity in a wire varies in direct proportion to the lengthlcm

of the wire. When the length is 10 cm, the resistance is 0 : 06 ohms. Find:

a the law connectingRandl

b the resistance when the wire is 50 cm long

c the length of wire which has a resistance of 3 ohms.

7 A 4 litre can of paint will cover 18 m^2 of wall. Ifnis the number of litres andAis the area covered,

write down a formula connectingAandn. Hence, find the number of litres required to paint a room

with wall area 40 : 5 m^2.

8 The speed of a falling object is directly proportional to the time it falls. The speed after 5 seconds is

49 m/s.

a What will be the speed of a falling object after 8 seconds?

b How long will it take a falling object to reach a speed of 100 m/s?

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y

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Variation and power modelling (Chapter 30) 607

IGCSE01

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Y:\HAESE\IGCSE01\IG01_30\607IGCSE01_30.CDR Monday, 27 October 2008 2:57:29 PM PETER