Work, Energy and Power Flashcards

1
Q

State the equation for Gravitational Potential Energy and define G.P.E.

A

G.P.E = mgh

G.P.E. is the energy a mass has due to its position in a gravitational field

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2
Q

Describe the change in G.P.E and K.E. for a falling object

A

As the object falls, its G.P.E decreases because it is converted to K.E. (in the form of velocity)
½mv² = mgΔh

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3
Q

Define work done

A

Work Done (energy transferred) = Force X distance moved in the direction of the force

W=Fs

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4
Q

Explain why the energy transferred in a falling object is equal to the work done.

A

Force (F) = Weight (mg)
Displacement (s) = change in height (h)
Therefore Fs = mgh

So W = mgh

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5
Q

Define a machine

A

Something that makes the work easier

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6
Q

Explain how a ramp/inclined plane acts as a machine

A

It allows a smaller force to be applied by ‘spreading it’ over a larger distance

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7
Q

What does the area under the curve show in a Force vs. Displacement graph?

A

Work Done (Energy Transferred)

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8
Q

Define Power and state the equation needed to calculate it

A

The rate of energy transfer

Power (J/s) = Work Done (J) / Time Taken (s)
P = W / t

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9
Q

Show that P = Fv

A
Power = Work / Time
Power = (Force X Displacement) / Time
Displacement / Time = Velocity 
Therefore Power = Force X Velocity
P = Fv
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10
Q

State the equation for Kinetic Energy

A

K.E. = ½mv²

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11
Q

Give the 6 forms of energy

A

1) Potential energy
2) Kinetic energy
3) Thermal energy
4) Chemical/nuclear energy
5) Electrical energy
6) Elastic energy

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12
Q

Define joules

A

A measurement of energy where 1 joule is equal to the energy needed to raise a 1N weight through a vertical height of 1m

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13
Q

State the principle of conservation of energy

A

Energy cannot be created or destroyed

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14
Q

Give the equation for the work done to stretch a spring to extension ΔL

A

Work done = ½FΔL

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15
Q

Define kinetic energy

A

The energy of an object due to its motion

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16
Q

Define potential energy

A

The energy of an object due to its position

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17
Q

Define thermal energy

A

The energy of an object due to its temperature

18
Q

Define chemical/nuclear energy

A

The energy associated with chemical or nuclear reactions

19
Q

Define electrical energy

A

The energy of electrically charged objects

20
Q

Define elastic energy

A

The energy stored in an object when it is stretched or compressed

21
Q

Give the equation for the kinetic energy of a pendulum bob at height h, released from height h₀

A

kinetic energy = loss of potential energy from maximum height
½mv² = mg (h₀ - h)

22
Q

Give 2 ways in which energy can be transferred from one object to another

A

1) Work done - by a force due to one object making the other object move
2) Heat transfer - from a hot object to a cold object. Heat transfer can be due to conduction, convection or radiation

23
Q

Give the 3 ways heat can be transferred

A

Conduction
Convection
Radiation

24
Q

State the name for the name for the output power of an engine

A

Motive power

25
Describe the resistive forces in relation to the motive force when an object moves at a constant velocity at constant height
The resistive forces (e.g. friction, drag, air resistance) are equal and opposite to the motive force
26
Give the equation for the power of an engine in terms of its velocity
Work done per second = force x distance moved per second | P = Fv
27
Describe the motion of an object when its output force exceeds the resistive forces on it
It speeds up
28
Give the equation for the motive power of an object in terms of energy wasted
Motive power = energy wasted per second (due to resistive forces) + Gain of kinetic energy per second
29
Give the equation for the output of a machine
P(out) = Work done by the machine / time taken Output power, P(out) = Fv where F = output force of machine and v = velocity of object
30
Define useful energy
The energy transferred for a purpose
31
Give the equation for efficiency of a machine
Efficiency = Useful energy transfered / energy supplied = work done / energy supplied = output power / input power
32
Give the equation for percentage efficiency of a machine
% Efficiency = efficiency x 100%
33
Give the average electrical power generated by a single wind turbine in a suitable location
2MW
34
Give the equation for the kinetic energy per second of the wind passing through a wind turbine
Kinetic Energy per second = ½ρv²vA = ½ρv³A where ρ is the density of air, v is the speed of the wind and A is the area of the cylinder of air passing through the turbine
35
Describe the principle of how hydroelectricity and tidal power stations work
They make use of the potential energy released by water when it runs to a lower level
36
Describe the difference between a tidal power station and a hydroelectric power station
Tidal power stations drop more water but over a smaller distance than a hydroelectric power station Tidal power stations release more energy per day
37
Explain why solar panels in space would absorb more solar energy than solar panels at the Earth's surface
Because some solar energy is absorbed in the atmosphere
38
Describe how a solar panels produces electricity
A solar panel produces electricity directly A potential difference is produced across each cell when light is incident on the cell This converts light energy into electrical energy
39
Give 2 ways in which energy demands could be reduced
Better insulation in homes and buildings | More efficient machines
40
Give 3 ways in which carbon emissions could be cut significantly
- Using more renewable sources of energy - Carbon capture of carbon emissions from fossil-fuel power stations - Road transport to be switched from fossil fuels