Energy Transfers Flashcards

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1
Q

What is the equation for gravitational
potential energy? Give SI units for all
quantities involved.

A

mgh

Mass x Gravitational Field Strength x
Height

Energy (J), Mass(kg), Gravitational Field Strength (N/kg)

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2
Q

What is the equation for kinetic energy? Give SI

units for all quantities involved.

A

½ m v²

½ x Mass x (Velocity)²

Energy (J), Mass(kg), Velocity(m/s)

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3
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

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4
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

KE (Kinetic Energy), GPE (Gravitational Potential Energy)

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5
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.

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6
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

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7
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

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8
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.

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9
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.

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10
Q

State two equations to calculate efficiency.

A

=Useful Output Energy / Total Input
Energy

=Useful Power Output/Total Power
Output

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11
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.

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12
Q

Do double-glazed windows have a higher or lower

thermal conductivity than single-glazed windows?

A

Lower, meaning less energy transfers

through them

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13
Q

State three methods of reducing heat

loss in a building

A
  1. Double glazing
  2. Loft and wall insulation
  3. Thicker walls
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14
Q

How can you reduce unwanted energy

transfer in a mechanical system?

A

Reduce friction by lubricating moving parts.

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15
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)

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