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physics paper 2 (complete) Flashcards

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1
Q

P8: Name the star in our solar system.

A

The Sun.

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2
Q

P8: How many planets in our solar system?

A

8

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3
Q

What is the difference between a moon and a dwarf planet?

A

What is the difference between a moon and a dwarf planet?

Dwarf planets orbit the sun; moons orbit planets.

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4
Q

What is the difference between a moon and a dwarf planet?

A

Dwarf planets orbit the sun; moons orbit planets.

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5
Q

P8: What do we call the natural satellites in the solar system?

A

Moons

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6
Q

P8: How was the sun formed, and what caused this to happen?

A

From a cloud of dust and gas (nebula); pulled together by

gravitational attraction; causing fusion reactions.

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7
Q

P8: List the major bodies found in the solar system.

A

Star, planets, dwarf planets, moons, asteroids, comets.

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8
Q

What is a nebula?

A

Cloud of dust and gas.

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9
Q

What determines the life cycle a star will take?

A

The size of the star.

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10
Q

Describe the lifecycle of a star the size of the sun.

A 
Cloud of gas and dust, 
protostar, 
main sequence star, 
red giant,
white dwarf, 
black dwarf.
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11
Q

Describe the lifecycle of a star more massive than the sun.

A 
Cloud of gas and dust, 
protostar,
main sequence star, 
red super giant, 
supernova, 
neutron star or black hole.
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12
Q

What processes produce all of the naturally occurring elements?

A

Fusion.

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13
Q

Where are elements heavier than iron produced?

A

supernova

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14
Q

How are these elements distributed throughout the universe?

A

Explosion of massive star (supernova).

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15
Q

What force enables planets and satellites to maintain their circular
orbits?

A

gravity

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16
Q

The international space station takes 92 mins to orbit the Earth.
The Moon takes 27.3 days to orbit the Earth. Explain why these
orbital times are different.

A

Moon orbits at a much greater distance than the ISS; it is much
further away from the Earth.
The further from the Earth the lower the gravitational attraction
So The Moon travels slower and it takes much longer to orbit
the Earth.

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17
Q

Explain how the Earth’s gravity can result in the

satellites velocity changing but not its speed.

A

In a circular orbit the speed of the satellite
remains constant. Velocity is a vector so has
size AND direction.
As the direction is changing, the velocity
must be changing.

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18
Q

Explain why satellites in a polar orbit must travel at much higher
speeds than a satellite in a geostationary orbit.

A

Polar satellite are in a much lower orbit than
geostationary satellites.
In a lower orbit, gravity has a much stronger
influence so the polar satellite must travel much
faster to avoid being pulled down to Earth.

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19
Q

Which colour of light has the longest wavelength?

A

red

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20
Q

The light reaching Earth from distant galaxies exhibits red shift.
Explain why red shift occurs.

A

Galaxy is moving away at high speed
Light waves from the galaxy are being stretched to longer wavelengths.
Longer wavelengths of light are found at the red end of the spectrum.
This shift of wavelength is called red shift.

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21
Q

If galaxy A has a much bigger red shift than galaxy B, what does this
tell you about galaxy A?

A

It is travelling away at a higher speed. It is further away.

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22
Q

Approximately how many years ago did the Universe begin?

A

14 billion

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23
Q

Describe the current theory of how the Universe began.

A

Started as a small region that was very hot and dense.

Big Bang caused it to rapidly expand.

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24
Q

Atoms are only thought to make up about 5% of the known Universe.
What do scientists think the remaining 95% is made up of?

A

Dark matter and dark energy.

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25
Q

P8: The most distant galaxies in the Universe are thought to be:

A

accelerating

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26
Q

P7: What are the poles of a magnet?

A

Places where the magnetic forces are strongest.

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27
Q

P7: When two magnets are brought together what do they do?

A

Exert a force on each other; attraction or repulsion.

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28
Q

P7: When a magnet and a magnetic material are brought together
what do they do?

A

ATTRACT

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29
Q

What is a permanent magnet?

A

Material that produces its own magnetic field.

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30
Q

P7: What is an induced magnet?

A

Material that becomes a magnet when it is placed in a

magnetic field.

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31
Q

P7: Describe the difference between permanent and induced

magnets.

A

Permanent produces its own field/ induced becomes
magnetic when placed in a field.
Permanent can attract or repel/ induced always attracts.
Induced magnet loses most/all of its magnetism quickly when
removed from magnetic field.

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32
Q

Which part of a magnet has the strongest magnetic field?

A

poles

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33
Q

Two magnets are placed close together, north seeking pole to
north seeking pole. Describe the forces acting on the two
magnets.

A

Repulsion.

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34
Q

Name three magnetic elements.

A

Iron, steel, cobalt, nickel.

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35
Q

Describe two methods for finding the magnetic field pattern

of a bar magnet.

A

Sprinkle iron filings onto paper, tap paper. Use small
compasses to follow field from poles; mark paper at the
compass needle end.

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36
Q

How would you describe the direction of a magnetic field

line?

A

Given by the direction of the force that would act on another
north pole placed at that point/ from the north (seeking) pole
to the south (seeking) pole.

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37
Q

What does a magnetic compass contain?

A

Small bar magnet.

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38
Q

Which way does the compass needle point?

A

In the direction of the Earth’s magnetic field.

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39
Q

What do scientists think is the cause of the Earth’s magnetic
field?

A

molten iron core

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40
Q

What is produced when a current flows through a

conducting wire?

A

Magnetic field.

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41
Q

What is produced when a current flows through a
conducting wire?
Magnetic field.
2. Name two factors which will impact on your answer to
question 1.

A

Current flowing through the wire, distance from the wire.

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42
Q
A

Coil of wire in which a magnetic field is created by passing a
current though it.

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43
Q

Describe the magnetic field inside a solenoid.

A

Strong and uniform.

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44
Q

State three ways of increasing the strength of the magnetic

field produced by a solenoid.

A

Increase the current

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45
Q

What is an electromagnet?

A

Solenoid with an iron core.

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46
Q

Describe how a relay works.

A

A switch; uses a solenoid to attract an iron armature; small

current turns on a larger current.

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47
Q

An electric bell uses a solenoid. Use the
diagram below, and your own knowledge, to explain how an
electric bell works.

A

Solenoid attracts an iron armature,
breaking the circuit.
Demagnetises, armature springs back.
Circuit reformed. Repeat.

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48
Q

Describe the motor effect.

A

Conductor carrying current placed in magnetic field; magnet
and conductor exert a force on each other; this force =
motor effect.

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49
Q

What 3 factors does Fleming’s left hand-rule represent?

A

The force, the current in the conductor, the magnetic field.

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50
Q

Give three ways of making the electric motor spin faster.

A

Increase the current;

increase the number of turns on the
coil;

increase the strength of the magnets.

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51
Q

A 40 cm piece of wire is placed in a magnetic field of
strength 0.4 T. The wire carries a current of 60 mA. Work out
the force on the wire using the equation: Force = magnetic
flux density x current x length.

A

0.0096 N
40 cm = 0.4 m
60 mA = 0.06 A
F = Bil F = 0.4 x 0.06 x 0.4 N

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52
Q

Explain how a loudspeaker works.

A

A fluctuating electric current flows through the coil of wire.
The coil of wire then becomes an electromagnet.
The electromagnet is then attracted or repelled away from
the magnet.
This causes the cone to move – producing a sound.

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53
Q

What does the term ‘induced current’ mean?

A

Current made by moving a conductor relative to a magnetic

field.

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54
Q

What is a simple generator made of?

A

Coil of wire; magnetic field, movement.

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55
Q

How can the size of the induced potential difference/

current in a generator be increased?

A

More turns, stronger magnetic field, increase sped of

movement.

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56
Q

What factors affect the direction of the induced potential

difference/ current?

A

Direction of movement/ rotation; reversing the polarity.

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57
Q

What type of current is induced by an alternator?

A

ac

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58
Q

What type of current is produced by a dynamo?

A

dc

59
Q

Describe two ways of reversing the direction of current

flow on a dynamo.

A

Swap the polarity of both magnets.

Spin the coil of wire in the opposite direction.

60
Q

At which point of the rotation does a dynamo induce the

greatest potential difference?

A

When the coil of wire is perpendicular to the magnetic
field; it is at this point that the magnetic field lines are
being cut at the greatest rate.

61
Q

How do microphones use the generator effect?

A

Convert the pressure variations in sound waves into

variations in current.

62
Q

What does a basic transformer contain?

A

Primary coil, secondary coil, iron core.

63
Q

Why are cores made of iron?

A

Easily magnetised.

64
Q

What can be said about the potential difference in the

primary and secondary coils of a step-down transformer?

A

Vs < Vp

65
Q

How do transformers work?

A

• Transformers have a primary coil of wire with an
alternating current (ac) flowing.
• This produces an alternating magnetic field in the iron
core.
• On the secondary side of the transformer there is a coil
of wire and an alternating magnetic field.
• So the magnetic field is moving relative to the coil of
wire.
• This induces a potential difference (and induces a
current if there is a complete circuit). This is the
generator effect.

66
Q

A step-up transformer is used in a power station to
increase the potential difference output from 25,000 V to
400,000 V. The current through the overhead power lines
is 25 A. Work out the current in the primary coil.

Vs × Is = Vp × Ip

A

400 A
16 times more potential difference so 16 times less
current.
Vs × Is = Vp × Ip or correct substitution.

67
Q

Why are transformers used when sending electricity

through the National Grid?

A

Increases potential difference; decreases current;

decreases loss of energy through heat.

68
Q

P6: What is meant by the period of a wave?

A

Time taken to complete 1 full wave.

69
Q

A wave has a period of 0.25s. Calculate the frequency of this wave.

A

f = 1/T f = 1 / 0.25 Frequency = 4Hz

70
Q

A sound wave has a frequency of 240Hz and a wavelength of 1.38m.
Calculate the velocity of this sound wave. Show clearly the formula
you use for this calculation.

A

v = f λ v = 240 x 1.38

Velocity of the wave = 331.3m/s

71
Q

The diagram shows a ripple tank, used to
generate waves in the laboratory.
Describe the measurements that must be made in
order to calculate the velocity of water waves in the tank.

A

Measure wave frequency with a strobe light and wavelength of a
wave with a ruler then use v = f λ
or: measure time for a wave to travel a measured distance and
use s = d/t

72
Q

The sound waves from a noisy jet travel from the

air into water. Which property of the wave will not change?

A

Frequency.

73
Q

The Eiffel Tower is made of iron. The speed of
sound in iron is 4000m/s. Someone at the top hits the iron with a
hammer and the sound can be heard at the bottom 0.08s later. How
tall is the Eiffel Tower?

A

s = d/t d(height) = s x t Height = 4000 x 0.08 = 320m

74
Q

When light strikes a black curtain, very little light gets

reflected. What happens to the light?

A

It is absorbed by the curtain as heat energy.

75
Q

Explain why you can not see your reflection when you

look into a piece of white plastic held in front of you.

A

.

Light rays are scattered in all directions – diffuse reflection.

76
Q

When waves flow from deep water to shallow water
the wave can bend (diffract). What happens to the speed of the
wave to allow this to happen?

A

Waves slow down in shallow water.
Bottom of wave enters shallow water before top
of wave. Therefore bottom of wave slows down
before the top, causing the wave to bend.

77
Q

Describe how sound waves in the air are

converted to vibrations in solids by the ear.

A

Compressions in the air cause the ear drum to flex inwards and
outwards. This sets up vibrations of the bones in the inner ear.

78
Q

Which of the following represents the frequency

range of human hearing?

A

20Hz to 20 000Hz

79
Q

What are ultrasound waves?

A

Sound waves with a frequency higher than humans can hear.

80
Q

The picture shows the
ultrasound image of an unborn baby.
Explain how ultrasound is able to produce
an image from the outside of the mother.

A

Ultrasounds penetrate the body. Some of the waves are reflected
when they meet a boundary between two structures. These
reflected waves are received at different times and are formed into
an image.

81
Q

p WAVES:

A

longitudinal waves
fastetst
can travel through liquid and solid

82
Q

.Describe how P and S seismic waves can be used

to show part of the Earth’s core is liquid.

A

Detectors on the opposite side of the Earth to the earthquake
epicentre can record both P and S waves. Only P waves are
detected meaning S waves can not penetrate through the Earth. As
S waves can not travel through liquids, it is deduced that part of
the core is liquid .

83
Q

P5: What is a scalar quantity?

A

Scalars quantities have magnitude ONLY i.e. no direction.

84
Q

P5: Explain how a car can be moving at a constant speed but have changing
velocity.

A

As velocity is a vector if the direction of the car changes the velocity will
change, at a constant speed.

85
Q 
State whether the following quantities are scalars or vectors::
acceleration
mass
momentum
time
A

Acceleration ; vector

mass: scalar
momentum: vector
time: scalar

86
Q

Gravity is a force that acts at a distance.

Name two other forces that act at a distance.

A

Magnetism
Electrical Force
Nuclear Force

87
Q

Name three contact forces.

A

Tension
Friction (including air resistance)
Normal Force

88
Q

A boy has a mass of 40 kg. Work out the boy’s weight.

Take g = 10 N/kg.

A

Using

W = mg

Substitution gives

W = 40 x 10

Answer

W = 400 N

89
Q

Name a piece of scientific equipment that you would use to find the
weight of a block in a science laboratory.

A

A newtonmeter

90
Q

On The Moon an astronaut has a weight of 130 N. The gravitational field
strength on The Moon is 1.7 N/kg. The gravitational field strength on the
Earth is 10 N/kg.
Work out the weight of the astronaut on the Earth.

A

Using W = mg
Mass of astronaut = 130 / 1.7
Mass of astronaut = 76.5 kg

Using W = mg
Weight of astronaut on Earth = 76.5 x 10
Weight of astronaut on Earth = 765 N

91
Q

A child cuts out a picture of a snowman on a piece of card.

Describe how you could determine the centre of mass of the snowman.

A

Hang the picture using a pin so that the shape is free to rotate.
Have a plumb line hanging from the pin.
Mark the path of the plumb line against the picture.
Hang the picture from another point.
Mark the path again.
Where the lines cross is the centre of mass of the picture.

92
Q

A piano is pushed across a wooden floor with a force of 2500 N.
The piano moves a distance of 3.5 m.
Work out the work done moving the piano.

A

Using W = F s
Work done = 2500 x 3.5
Work done = 8750 J

93
Q

Work done is usually measured in joules. An alternative unit for
work done is

A

Nm

94
Q

Why does a bicycle pump get hot when used to pump up a tyre?

A

Work is done in compressing the air
Causing the molecules to increase the frequency of their collisions
Causing frictional heating and an increase in the temperature.

95
Q

A box with a weight of 120 N is lifted up 1.8 m onto a shelf.
Calculate the work done in lifting the box.

A

Using Work done = force x distance
Work done = 120 x 1.8
Work done = 216 J

96
Q

When a book is lifted 3 m the work done on the book is 12.6 J.
Calculate the weight of the book.

A

Using

Work done = force x distance

Rearranging gives

Force = work done / distance

Substitution gives

Force = 12.6 / 3

Answer

Force = 4.2 N

97
Q

What type of energy is stored in a stretched spring?

A

Elastic Potential Energy

98
Q

What is the least number of forces required to stretch a spring?

A

2

99
Q

A spring is stretched beyond its elastic limit. Describe the effect that this
would have on the spring.

A

The spring would be inelastically deformed

so would not return to its original shape

100
Q

Explain how the extension of a spring is determined.

A

The length of the extended spring

minus the original length

101
Q

Motorcycles use springs for their suspension.
The spring is compressed when the motorcycle rides over bumps.
A force of 240 N compresses the spring 2 cm.
Calculate the spring constant of the motorcycle spring in N/m.

A

Using F = k e
Rearranging gives k = F/e
Substitution gives k = 240 / 0.02
Spring constant is 12 000 N/m

102
Q

In a bath full of water a force of 1250 N acts on an area of 0.5 m 2 at the bottom of the bath.
Calculate the pressure acting on the bottom of the bath.

A 
Pressure = Force / Area
Pressure = 1250 / 0.5
Pressure = 2500 Pa
103
Q

A pressure of 4000 Pa acts in a hydraulic brake fluid. The surface of the
slave cylinder inside the brake system has a surface area of 0.03 m
2
.

Calculate the force acting on the slave cylinder.

A 
Pressure = Force / Area
Force = Pressure x Area
Force = 4000 x 0.03
Force = 120 N
104
Q

A beaker is filled to a depth of 10 cm with water. Water has a density of
1000 kg/m3. Calculate the pressure acting at the bottom of the beaker.

Take g = 10 N/kg.

A

Convert 10 cm into standard units: 10 cm = 0.1 m
Pressure = height of column x density x gravitational field strength
Pressure = 0.1 x 1000 x 10
Pressure = 1000 Pa

105
Q

A scuba diver is diving in the sea. The pressure acting on the scuba diver is
267 800 Pa. Salt water has a density of 1030 kg/m3.

Calculate the depth of the scuba diver.

A

Pressure = height of column x density x gravitational field strength

Rearranging gives

Height of column = Pressure / (density x gravitational field strength)
Height of column = 267 800 / (1030 x 10)
Height of column = 26 m
Therefore the scuba diver is at a depth of 26 m.

106
Q

A boat floats in sea water (density = 1030 kg/m3). The boat has a surface
area of 15 m2 in contact with the water and has a pressure of 4120 Pa acting on it.
Find the depth the boat floats at.
Take g = 10 N/kg.

A

Pressure = height of column x gravitational field strength x density
4120 = height of column x 10 x 1030
4120 / (10 x 1030) = height of column
Height of column = 0.4 m
Therefore the depth of the boat is 0.4 m.

107
Q

Explain why the atmospheric pressure on the top of Mount Everest is
lower than the atmospheric pressure at sea level.

A

At sea level there is more air above you
This gives a greater weight of air pushing on you per unit area
Increasing the pressure

108
Q

State the typical speed of a person

a) walking
b) cycling

A

a) walking - 1.5m/s

b) cycling - 6m/s

109
Q

State the equation that links speed, distance and time.

A

speed = distance / time

110
Q

Describe the difference between speed and velocity.

A

Speed is a scalar quantity – it has magnitude but no direction.
Velocity is a vector – it has magnitude and direction.

111
Q

A car moves round a circular track at 120 mph.

Give the average velocity of the car. Explain your answer.

A

Average velocity is 0 m/s
As on completion of every lap the car has a displacement of 0 m
and velocity is found using displacement / time
the average velocity must be 0 m/s

112
Q

A motorcycle travels a distance of 420 miles in 8.5 hours.

Give the average speed of the motorcycle.

A 
speed = distance / time
speed = 420 / 8
speed = 52.5 mph
113
Q

Describe the difference between instantaneous speed and average
speed.

A

Instantaneous speed is the speed at a given moment in time.
Average speed is the speed over the whole journey including periods
of acceleration and deceleration.

114
Q

Describe how you would find the instantaneous speed of an object from
a distance‐time graph where the line is a curve.

A

Draw the tangent to the curve.

Find the gradient of the line you have
drawn.

The gradient of the line is the
instantaneous speed.

115
Q

State the equation that links acceleration, change in velocity and time
taken.

A

acceleration = change in velocity / time taken

116
Q

Describe what is meant by a negative acceleration.

A

A negative acceleration means that the object is slowing down or
speeding up in the opposite direction (to that which has been assumed
to be positive).

117
Q

Give the units of acceleration.

A

m/s2 or m/s/s or ms‐2

118
Q

Describe how the distance travelled by an object can be found from a
velocity‐time graph.

A

The area under the line on a velocity‐time graph represents the distance
travelled by that object.

119
Q

A stone is dropped off a cliff.
The stone hits the floor at 30 m/s.
Calculate the height of the cliff.
Take g = 9.8 m/s2

A

Since the stone is dropped u = 0 m/s

Using v2 – u2 = 2 a s
Substituting gives 302 – 02 = 2 x 9.8 x s
Simplifying gives 900 = 19.6 x s
Rearranging gives 900 / 19.6 = s

Therefore s = 45.9 m

120
Q

Explain how the motion of a skydiver changes from the moment they
jump out of the plane until they land.

A

• Skydiver accelerates due to gravity (at a rate of 10 m/s2)
• As the skydiver picks up speed the drag they experience increases
• But the gravitational attraction stays the same
• so the acceleration of the skydiver decreases in size.
• When drag and weight are equal in size but opposite in direction the
skydiver will fall with terminal speed
• as there is no resultant force so no acceleration
• When the parachute is opened there is an increase in drag
• Decelerating the skydiver
• Until weight and drag are equal in size but opposite in direction
• Then the skydiver falls at a new (lower) terminal speed
• Which is lower as the the large surface area of the parachute increases
the amount of drag at a given speed.
• Skydiver decelerates to 0 m/s when they hit the ground.

121
Q

Describe why a cannon ball, when fired from a cannon does not continue
to move with constant velocity.

A

• Gravity acts pulling the cannon ball downwards
• So, there is a resultant force
• Objects will only continue with uniform motion when no resultant force
acts.

122
Q

What is inertia of an object a measure of?

A

How easy, or difficult, it is to get the object to change its motion.
The more inertia an object has the harder it is to get it to change its
motion.

123
Q

State the equation commonly used for Newton’s second law

A

force = mass x acceleration

124
Q

A car has an acceleration of 1.7 m/s2 and a mass of 700 kg.

Calculate the driving force of the car.

A

Using F = m a
force = 700 x 1.7
force = 1190 N

125
Q

A skydiver has a weight of 686 N and a mass of 70 kg.
Calculate the acceleration of the skydiver the moment he jumps out of
the plane.

A 
acceleration = force / mass
acceleration = 686 / 70
acceleration = 9.8 m/s2
126
Q

A motorcycle has a driving force of 1400 N and an acceleration of 6 m/s2.
Calculate the mass of the motorcycle.

A 
mass = force / acceleration
mass = 1400 / 6
mass = 233 kg
127
Q

A father and his daughter were ice skating.
The father has a mass of 75 kg and his daughter has a mass of 30 kg.
The father pushed his daughter and she feels a force of 50 N.
Calculate the force on the father.

A

50 N
From Newton’s third law: whenever two objects interact, the forces they
exert on each other are equal in size and opposite in direction.

128
Q

A car crashed into a crash barrier. The force exerted by the barrier on the
car was 4500 N. Describe the force exerted by the car onto the barrier.

A

The force exerted by the car onto the barrier is 4500 N.
From Newton’s third law: whenever two objects interact, the forces they
exert on each other are equal in size and opposite in direction.

129
Q

Define thinking distance.

A

The distance travelled while the driver reacts to a stimulus until the
driver gets their foot onto the brake pedal (but before the brake pedal is
pressed).

130
Q

Complete the equation:

stopping distance =

A

stopping distance = thinking distance + braking distance

131
Q

Describe how the speed of a vehicle affects the thinking distance.

A

Increasing speed increases thinking distance

Doubling your speed doubles the thinking distance.

132
Q

A driver sees a car braking sharply in front of him. The driver takes 0.5 s
to react to the stimulus and then brakes. Figure 1 shows the velocity‐
time graph for the motion of the vehicle from seeing the stimulus to
stopping. Calculate the stopping distance of the vehicle.

A

stopping distance = area under line

stopping distance = Area A + Area B

stopping distance = 5 + 5

stopping distance = 10 m

133
Q

Describe how you could measure the reaction time of a person.

A

• Get the person to stand with their hand open
• Place a ruler at the top a the person’s hand
• Drop the ruler through their hand
• When the person sees the ruler move they
need to close their hand
• The distance the ruler travels corresponds to the
thinking distance

134
Q

Explain the dangers caused by large decelerations of a vehicle.

A

• Large decelerations can cause the brakes to overheat and become less
effective
• Large decelerations can also cause a loss of control
• Large decelerations can also exert large forces of people within a vehicle.

135
Q

Put the following factors under the correct headings to show whether the factor affects think distance, braking distance or both thinking and braking
distance.

Speed
Mass
Icy roads
Tiredness

Poor brakes
Mobile Phone use
Alcohol
Bad tyres

A

Thinking distance:
-Tiredness, mobile phone use and alcohol.

Braking distance:
- mass, icy road, poor brakes and bad tyres

both:
- speed

136
Q

State the units of momentum.

A

kgm/s

137
Q

State the equation that links mass, momentum and velocity.

A

Momentum = mass x velocity

138
Q

Momentum is a conserved quantity.

Explain what is meant by a conserved quantity.

A

The momentum before and after an event is equal in a closed

system

139
Q

A football has a mass of 0.75 kg and is kicked with a speed of 12 m/s.
Calculate the momentum of the kicked football.

A

Using momentum = mass x velocity
Momentum = 0.75 x 12
Momentum = 9 kgm/s

140
Q

Two ice skaters push themselves apart on the ice.

Explain how the conservation of momentum applies in this case.

A

The momentum before pushing is 0 kgm/s as they are not moving
On pushing apart the momentum of each ice skater is the same size
but in the opposite direction
When adding (vector addition) of the momentum of the two ice
skaters sum is also 0 kgm/s
So momentum is conserved.

141
Q 
A trolley has a mass of 1.2 kg and a
speed of 4.5 m/s. The trolley crashes
into a stationary trolley of mass 0.8 kg.
On impact the two trolley’s stick
together and move off with speed, v.

a. Calculate the momentum of the trolleys
before impact.

A

Using momentum = mass x velocity
momentum = 1.2 x 4.5
momentum = 5.4 kgm/s

142
Q 
A trolley has a mass of 1.2 kg and a
speed of 4.5 m/s. The trolley crashes
into a stationary trolley of mass 0.8 kg.
On impact the two trolley’s stick
together and move off with speed, v.

B) Calculate the speed of the trolleys after
impact.

A

Using conservation of momentum; Momentum before = Momentum after
5.4 = massafter x velocityafter
velocityafter = 5.4 / 2 = 2.7 m/s

143
Q

A gymnast falls onto a crash mat. The crash mat reduces the risk of
injury to the gymnast.

Explain how the crash mat reduces injury.

A

The crash mat increases the time taken to come to a stop
This decreases the acceleration
Since F = m△v △t
This reduces the force acting on the gymnast

144
Q

A car of mass 850 kg hits a crash barrier at a speed of 30 m/s. The car
stops in 0.4 s. Calculate the force on the car.

A

Using F = m X △v /△t
F = 850 x 30 0.4
F = 63 750 N

SCIENCE (5 decks)

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