Energy Changes Flashcards

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1
Q

State the law of energy conservation.

A

Energy cannot be created or destroyed
(it can only be transferred into different
forms).

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2
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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3
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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4
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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5
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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6
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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7
Q

Describe the energy changes in a power station.

A

● Heat energy released in the reaction heats water to
make steam
● Steam moves the turbine, converting into kinetic energy
● Kinetic energy turns the generator
● Electrical energy as the generator generates
electricity

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8
Q

In what ways can the energy of a system be

changed?

A

● Through work done by forces
● Through electrical input
● Through heating

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9
Q

How can energy be changed through work done by

forces?

A

A force which moves an object (kinetic
energy) causes work to be done over a
distance.

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10
Q

What equation is used to measure the work done on

an object?

A
Work done (J) = force (N) x distance (m)
W = Fd
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11
Q

Why do wasteful mechanical processes cause a rise

in the temperature of the surroundings?

A

They cause energy to be transferred by heating the surroundings.

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12
Q

What is the equation for kinetic energy? Give SI

units for all quantities involved.

A

E = ½ m v^2

Energy = ½ x Mass x (Velocity)²

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

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13
Q

What is the equation for gravity potential energy?

Give SI units for all quantities involved.

A

E = mgh

Energy = Mass x Gravitational Field Strength x Height

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

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