Answers to end-of-chapter questions
Chapter 3
11 a weight = mass × g
1 A force can make an object change direction,
= 80 × 10
= 800 N
decelerate, or accelerate.
2 resultant force
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3 weight
b the same
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4 a force = mass × acceleration
c less
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12 a the two 5000 N forces
b, c
Quantity
Unit
Scalar or vector?
mass
kg
scalar
acceleration
m/s2
vector
force
N
vector
They are equal in size but act in
opposite directions.
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c The lorry will speed up (accelerate).
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= 20 × 5
= 100 N
6 a weight downwards, air resistance upwards
c The resultant force on it is zero, so it does not
accelerate.
force
mass
1 400 000
=
800 000
d terminal velocity
= 1.75 m/s2
14 acceleration =
b zero
7 a impulse of force = change of momentum
b F = force, t = time, m = mass, v = final velocity,
u = initial velocity
15 acceleration =
=
c Momentum is a vector quantity.
8 a kilogram (kg) or gram (g)
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b newton (N)
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c metre per second per second (m/s2)
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direction (like an arrow).
b Mass is not a vector quantity (it is a
scalar), so it does not have direction.
10 the bigger force acting on the smaller mass,
that is, the 10 N force acting on the 5 kg mass
© Cambridge University Press 2014 IGCSE Physics
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change in speed
time
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(20 – 12)
6.4
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= 1.25 m/s2
force = mass × acceleration
= 1200 × 1.25
= 1500 N
16 weight = mass × g
9 a Force is a vector quantity, that is, it has
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b resultant force = 1300 – 1200
= 100 N
forwards (to the left)
13 force = mass × acceleration
5 90°
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= 50 × 1.6
= 80 N
17 a resultant force = 680 – 600
= 80 N
upwards
b He will accelerate upwards.
Answers to end-of-chapter questions: Chapter 3
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1
18 a i (engine) thrust and (air) friction
ii force shown vertically upwards,
anywhere on plane
b i speed = distance in any form
time
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= 2200
2 75
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= 800 (km/h)
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ii idea of headwind on outward journey
or tailwind on return journey or routes
of different lengths or less friction or
less weight
© Cambridge University Press 2014 IGCSE Physics
19 a i
(v − u)
or v or 8
3
t
t
= 2.7 m/s2
ii F = ma or 42 × 8/3
= 112 N
iii distance in first 3 s = 12 m
so distance in last 11.2 s = 88 m
so final speed = 88 = 7.9 m/s
11.2
b Any two from: lower top speed, longer total
time, less steep slope at first, etc.
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Answers to end-of-chapter questions: Chapter 3
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