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Physics > Topic 1: Motion Forces and Conservation of Energy > Flashcards

Topic 1: Motion Forces and Conservation of Energy Flashcards

1
Q

What is a scalar quantity?

A

● A quantity that only has a magnitude

● A quantity that isn’t direction dependent

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2
Q

What is a vector quantity?

A

A quantity that has both a magnitude and an associated direction.

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3
Q

How can a vector quantity be represented?

A

Using vector arrows.

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4
Q

How do vector arrows represent vectors?

A

● The length of the arrow represents the magnitude

● The arrow points in the associated direction

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5
Q

Give three examples of vector quantities.

A
  1. Velocity
  2. Displacement
  3. Force
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6
Q

Give examples of scalar quantities.

A 
● Temperature
● Time
● Mass
● Speed
● Distance
● Energy
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7
Q

What is velocity?

A

The speed of an object in a specific direction.

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8
Q

Give an equation relating average speed, distance and time.

A

average speed = distance / time

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9
Q

On a distance/time graph, what value

does the gradient of the line represent?

A

The speed.

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10
Q

On a displacement/time graph, what

value does the gradient of the line represent?

A

The velocity.

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11
Q

What must be done to calculate speed at

a given time from a distance-time graph for an accelerating object?

A

● Draw a tangent to the curve at the
required time
● Calculate the gradient of the tangent

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12
Q

State the equation for the average acceleration of an object. Give appropriate units.

A

Acceleration = (Change in Velocity)/(Time Taken)

Acceleration (m/s2), Velocity (m/s), Time (s)

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13
Q

How can the distance travelled by an

object be calculated from a velocity-time graph?

A

It is equal to the area under the graph.

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14
Q

On a velocity/time graph what does the gradient of the graph represent?

A

The acceleration.

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15
Q

State a typical value for the speed of sound.

A

330 m/s

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16
Q

What is a typical value for human walking speed?

A

1.5 m/s

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17
Q

What is a typical value for human running speed?

A

3 m/s

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18
Q

What is a typical value for human cycling speed?

A

6 m/s

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19
Q

Give an approximate value for the
acceleration of an object in free fall
under gravity near the Earth’s surface.

A

10 m/s2

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20
Q

What is the name given to the single
force that is equivalent to all the other
forces acting on a given object?

A

The resultant force.

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21
Q

State Newton’s first law for a stationary object.

A

If the resultant force on a stationary

object is zero, the object will remain at rest.

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22
Q

State Newton’s first law for a moving object.

A

If the resultant force on a moving object
is zero, the object will remain at constant
velocity (same speed in same direction).

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23
Q

State the defining equation for Newton’s

Second Law.

A

Resultant force = Mass x Acceleration

F = ma

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24
Q

State Newton’s Second Law in words.

A

An object’s acceleration is directly
proportional to the resultant force acting
on it and inversely proportional to its
mass.

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25
Q

What is weight?

A

The force that acts on an object due to

gravity and the object’s mass.

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26
Q

What quantities does weight depend on?

A

Weight = mass x gravitational field strength

● The object’s mass
● The gravitational field strength at the
given position in the field

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27
Q

What is the unit used for weight?

A

The Newton (N).

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28
Q

What is the unit used for gravitational field strength?

A

N/kg

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29
Q

What piece of equipment can be used to

measure an object’s weight?

A

A calibrated spring-balance or newton-

meter.

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30
Q

When can an object travelling at a

constant speed not have a constant velocity?

A

When the object is changing direction; for example, moving in a circle.

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31
Q

Why does an object travelling at a
constant speed in a circle not have a
constant velocity?

A

● Speed is a scalar quantity
● Velocity is a vector quantity which means it can
only be constant if the direction is constant
● In circular motion, the direction is continuously
changing
● Velocity is constantly changing

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32
Q

What is the resultant force that acts on
an object moving in a circle called, and in
which direction does it act?

A

It is called the centripetal force and acts

towards the centre of the circle.

33
Q

What is inertial mass?

A

● A measure of how difficult it is to
change a given object’s velocity
● The ratio of force over acceleration

34
Q

State Newton’s Third Law.

A

Whenever two objects interact, the
forces that they exert on each other are
always equal and opposite.

35
Q

State the equation used to calculate an

object’s momentum.

A

Momentum = Mass x Velocity

36
Q

What is the unit used for momentum?

A

kgm/s

kilogram metres per seconds

37
Q

In a closed system, what can be said
about the momentum before and after a
collision?

A

The total momentum before and after are equal.

38
Q

State an equation linking change in

momentum, force and time.

A

Force x Time = Change in Momentum

F Δt = mΔv

39
Q

How can you measure human reaction

times?

A

● Using the ruler drop test
● Person A and B hold each end of a ruler with the 0 cm mark at the bottom
● Person A drops the ruler without telling person B
● Person B catches it
● The distance travelled corresponds to their reaction time

40
Q

Why is it important that the 0cm mark is

at the bottom?

A

So you can obtain the distance directly
without having to calculate it; otherwise,
a zero error would need to be accounted
for.

41
Q

What is the stopping distance of a

vehicle equal to?

A

The sum of thinking distance and braking

distance.

42
Q

For a given braking distance, if the
vehicle’s speed is increased, what can
be said about its stopping distance?

A

The stopping distance is increased with an increase in speed.

43
Q

Give a typical range of values for human

reaction time.

A

0.2 seconds - 0.9 seconds

44
Q

Give three factors which can affect a

driver’s reaction time.

A
  1. Tiredness
  2. Drugs
  3. Alcohol
45
Q

Give two factors which may affect

braking distance.

A
  1. Adverse (wet/icy) road conditions

2. Poor tyre/brake conditions

46
Q

Describe the energy transfers that take

place when a car applies its brakes.

A

● Work is done by the friction force between
the brakes and wheel
● Kinetic energy of the wheel is converted to
heat and is dissipated to the surroundings
through the brake discs

47
Q

To stop a car in a given distance, if its
velocity is increased, what must happen
to the braking force applied?

A

The braking force must also be

increased.

48
Q

State two consequences of a vehicle

undergoing very large decelerations.

A
  1. Kinetic energy converted to heat is
    very high causing brakes to overheat
  2. Loss of control of the vehicle
49
Q

What is the equation for kinetic energy?

A

1⁄2 m v2

50
Q

What is the equation for gravitational

potential energy?

A

Mass x Gravitational Field Strength x Height

51
Q

What is meant by the conservation of energy?

A

● The total amount of energy in a closed system remains constant
● Energy cannot be made or destroyed but
can change from one form to another

52
Q

Describe the energy changes involved
when a ball is thrown upwards and then
returns to its starting position. Ignore air
resistance.

A

● Upwards: KE is converted to GPE
● Peak: Maximum GPE, zero KE
● Downwards: GPE is converted to KE

53
Q

State any changes in the total energy of
a ball that is kicked, assuming that no
external forces act.

A

The total energy of the system remains

constant due to the conservation of energy.

54
Q

Describe the energy changes that occur

in a filament light-bulb.

A

● Electrical energy is transferred into
light and heat energy
● Light is a useful energy form, heat is
waste energy

55
Q

Describe the energy transfers for a

bungee jumper.

A

● When falling, the GPE is converted to KE of
jumper
● As the cord tightens, KE is converted and
stored as Elastic Potential Energy (EPE)
● At lowest point, the jumper’s initial GPE
equals the EPE stored in the cord

56
Q

Explain why a bungee jumper slows

down once the cord begins to stretch.

A

● Kinetic energy decreases since it is
converted to elastic potential energy
● Since KE is proportional to (velocity)2,
as KE decreases, so does velocity.

57
Q

What is waste energy?

A

The energy that is not used by the device
for its desired purpose, or not converted
into the desired form.

58
Q

State two equations to calculate

efficiency.

A

=Useful Output Energy / Total Input
Energy

=Useful Power Output/Total Power
Output

59
Q

State the consequence for energy transfer of a material with a high thermal conductivity.

A

The rate of energy transfer through the
material is higher than for a material with
a lower thermal conductivity.

60
Q

Do double-glazed windows have a
higher or lower thermal conductivity than
single-glazed windows?

A

Lower, meaning less energy transfers

through them.

61
Q

State three methods of reducing heat

loss in a building.

A
  1. Double glazing
  2. Loft and wall insulation
  3. Thicker walls
62
Q

How can you reduce unwanted energy

transfer in a mechanical system?

A

Reduce friction by lubricating moving parts.

63
Q

How can the efficiency of a system be

increased?

A
  1. Reducing waste output (by
    lubrication, thermal insulation etc.)
  2. Recycling waste output (eg. recycling
    thermal waste energy as input energy)
64
Q

What is a renewable energy resource?

A

An energy source which can be

replenished as it is being used up.

65
Q

Give four examples of renewable energy

resources.

A
  1. Wind Energy
  2. Hydro-Electricity
  3. Tidal Energy
  4. Solar Energy
66
Q

Give an example of a non-renewable

energy resource.

A

Fossil fuels (for example coal, oil and gas).

67
Q

What are the advantages of generating

power using gas rather than coal?

A

● Flexible Generation: Gas power
stations have short start-up times so
can be switched on/off more readily
● Lower emissions of carbon dioxide

68
Q

State two disadvantages of using
renewable energy resources to generate
power.

A

● Output often determined by external factors
(like wind speed), so supply is uncertain
● Renewable fuels often produce less energy
per kg (so are less economical).

69
Q

Explain the environmental impacts of

burning fossil fuels.

A

● Carbon Dioxide contributes to the
greenhouse effect, and causes global
warming

● Sulphur Dioxide leads to acid rain, which
can damage buildings and crops

70
Q

State three advantages of fossil fuels as

an energy resource.

A
  1. Reliable: Not dependent on external factors
    so can generate power anytime
  2. Produce large amounts of energy per kg
  3. Still relatively abundant, so cost-effective
71
Q

State three advantages of nuclear

power.

A
  1. Very large amounts of energy per kg of fuel
  2. No greenhouse gases released, so doesn’t
    contribute to climate change
  3. Low fuel costs
72
Q

State three disadvantages of nuclear

power.

A
  1. Produces nuclear waste which is harmful to
    humans & must be safely stored for centuries.
  2. Non-Renewable energy source
  3. Risk of nuclear accidents, which have fatal
    consequences on humans and the
    environment
73
Q

Give examples of social factors to

consider in energy production.

A

● Visual Pollution
● Sound Pollution

( both of these are disadvantages of wind farms)

74
Q

How does hydroelectric power produce

energy?

A 
● Rainwater collects behind a dam
● When this water is released, it is used
to turn a turbine
● This turbine turns a generator which
produces electricity
75
Q

What are some disadvantages of using

biofuels?

A

● When plants are burned/decay they release CO2
● In order to grow biofuels, you need to destroy land:
○ Habitat destruction
○ CO2 released when plants are cleared (for example, if they are burned)
● Growing biofuels reduces the land available for food crops

76
Q

What are the advantages of tidal energy

sources?

A

● No greenhouse gases
● Fairly reliable - tides occur twice a day
● Cheap to run as tides are natural, so
free

77
Q

What are the disadvantages of

hydroelectric power?

A

● The dam may cause flooding
● It can cost a lot to install the required
infrastructure

78
Q

What are some advantages of solar

panels?

A 
● They don’t cause harm to the
environment
● They are a renewable resource
● They can be used in remote areas where
other types of energy are less accessible

Physics (7 decks)

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