Page 26 - 新思维数学活动用书7 样章

2.2 Using expressions and formulae

Challenge

12 The weight of an object is calculated using the formula W = mg, where:
W is the weight, in newtons (N)
m is the mass, in kg
g is the acceleration due to gravity, in m/s 2

On Earth g = 10 m/s , and on the Moon g = 2 m/s .
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2
The mass of a man is 75 kg and the mass of a lunar landing module is 10 344 kg.
a Work out the weight of the:
i man on Earth ii lunar landing module on Earth.

b Work out the weight of the:
i man on the Moon ii lunar landing module on the Moon.
13 What value of x can you substitute into each of these expressions to give you the same answer?
x + 12 4x 6x − 8

14 Kwame uses the formula F = ma, where:
F is the force, in newtons (N)
m is the mass, in kg
a is the acceleration, in m/s 2

He works out that F = 75 N when m = 25 kg.
What value of a did he use? Explain how you worked out your answer.
15 This is part of Kali’s homework. She has spilt tea on some of her work.

Question
Use the formula M =
to work out the value of M when:

i P = 51 and h = 17 ii P = 65 and h = 13
Solution
i M = = 3 ii M = = 5

a What is the formula that Kali uses?
b Work out the value of M when P = 56 and h = 4.

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