Topic 8 – Energy: Forces Doing Work- 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

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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 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)

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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 = 1⁄2 m v2

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13
Q

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

A

E = mgh

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