General Physics 1.7 Energy, Work & Power Flashcards

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1
Q

What type of energy is stored in a moving object?

A

Kinetic energy.

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2
Q

What happens, in terms of energy, when an object is lifted?

A

Its gravitational potential energy increases.

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3
Q

Give an equation for kinetic energy

A

kinetic energy (J) = ½ × mass (kg) × velocity^2 (m/s)
E = ½mv^2

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4
Q

Give an equation for gravitational potential energy

A

Gravitational potential energy (J) = mass (kg) x
height (m) x gravitational field strength (N/kg)
E = mgh

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5
Q

When work is done against friction or resistance, what happens?

A

There is less of a change in kinetic energy because some energy is dissipated through heating.

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6
Q

What is the original source of most of the energy on Earth?

A

The sun.

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7
Q

What forms of energy do not ultimately come from the sun?

A

• Geothermal
• Nuclear
• Tidal

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8
Q

What is the source of the sun’s energy?

A

Nuclear fusion.

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9
Q

What are the main energy resources available to humans?

A

Fossil fuels (oil, gas and coal), nuclear fuels, biofuels, wind, hydroelectricity, tides and solar energy.

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10
Q

Define renewable energy.

A

Energy from a source which does not run out, so can be replenished.

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11
Q

Which energy sources are non-renewable?

A

• Fossil fuels
• Nuclear fuel

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12
Q

Which energy sources are renewable?

A

• Biofuels
• Wind
• Hydroelectric and tidal energy
• Geothermal energy
• Solar power

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13
Q

Why is non-renewable energy used to provide electricity on a large scale?

A

Non-renewable sources tend to have a larger energy output per kilogram of fuel.

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14
Q

What is efficiency?

A

The ratio of useful work done to energy supplied, often given as a percentage, i.e. the percentage of energy which is converted to a useful form.

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15
Q

Give the equation for efficiency

A

Efficiency =Useful energy output / Total energy input
You can convert this to a percentage by multiplying the answer by 100.

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16
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)
17
Q

Define work done.

A

• Work is done on an object when energy is transferred (from one form to another)
• Equal to the product of force and distance

18
Q

Give the equation for work done

A

work done (J) = force (N) × distance (m)
W= Fd
(where distance is the distance moved along the line of action of the force)

19
Q

Define power.

A

Power is the rate at which energy is transferred or the rate at which work is done.

20
Q

Give 2 equations for power

A

power (W) = energy (J) ÷ time (s)
power (W) = work done (J) ÷ time (s)