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physics a - level > Mechanics and Materials (5): Work, Energy and Power > Flashcards

Mechanics and Materials (5): Work, Energy and Power Flashcards

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1
Q

What are the 4 types of energy stores that you need to know about?

A
  • Gravitational potential - the position of objects in the gravitational field
  • Chemical - In bonds/batteries
  • Kinetic store - moving objects
  • Thermal store - hot objects
  • Elastic store - objects compressed or stretched
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2
Q

What are the 3 types of energy transfers that you need to know about?

A
  • Radiation (light, EM radiation etc.)
  • Electrically
  • Heat (hot object to a cold object vie conduction, convection or radiation)
  • Mechanically (work done by one object to make another move)
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3
Q

What is the unit of energy?

A

Joule, J

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4
Q

State the principle of conservation of energy

A

Energy cannot be created or destroyed, when energy is transferred the total amount of energy before is equal to the total amount of energy after

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5
Q

Work done on an object = …?

A

energy transferred to that object

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6
Q

What is the equation for the work done on an object that has a force, F applied to it for a distance, d?

A

W = Fd

where d is the distance moved in the direction of the force

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7
Q

What is the equation for the work done on an object when a force is applied to it at an angle?

A

W = Fscos(theta)

Where Fcos(theta) is the component of the force applied in the direction that the object is moving

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8
Q

What does the area under a force-distance graph when a constant force is applied represent?

A

The total work done on that object

  • As W = Fs
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9
Q

How do you calculate the work done from a force-distance graph where the force applied to the object is varied?

A
  • Split the area under the graph into rough strips
  • Determine the work done for each of the strips using W = F(delta)s
  • Add the individual work done’s to obtain total work done on the object by the force
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10
Q

State Hooke’s Law

A

The force needed to stretch a spring is proportional to the extension of that spring

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11
Q

What is the extension of a spring?

A

The difference in from the initial length of the spring to its length after the force has been applied

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12
Q

What is a force-extension graph the same as?

A

force-distance graph

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13
Q

What is the area under a force-extension graph equal to?

A

The work done applied to the spring

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14
Q

For a spring that obeys Hooke’s Law, how to you calculate the work done on the spring?

A

W = 1/2F(delta)L

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15
Q

What is the equation for the kinetic energy of an object?

A

Ek = 1/2mv^2

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16
Q

When does the equation for kinetic energy of an object not stand?

A

When the speed of the object is close to the speed of light

17
Q

What is the definition of potential energy?

A

The energy of an object due to its position

18
Q

What is the equation for GPE?

A

mg(delta)h

19
Q

When does the equation for GPE not stand?

A

When the change in height, h is much smaller that the radius of the body that produces the gravitational field strength -> otherwise the value of g will vary across the height that the object travels

20
Q

What is the relationship between GPE and KE?

A

KE = loss of potential energy/GPE

21
Q

What is the equation for the work done to overcome friction and air resistance for an object that goes from a higher height to a lower height?

A

W = GPE - KE

  • the difference between the two values is the energy lost to friction and air resistance
22
Q

What is the definition of power?

A

The rate of energy transfer per unit time

23
Q

What is the unit of power?

A

Watts, W

24
Q

What is the equation for power (energy transfer)?

A

P = (delta)E/t

25
Q

What is the equation for power (force doing work)?

A

P = (delta)W/t

26
Q

What is the equation for the power output of an object driven by a constant force, F at a velocity, v? How do you derive it?

A

P = Fv

P = W/t
W = Fs
P = Fs/t
P = Fv

27
Q

What is the equation for the motive power,P for a car?

A

Motive power = energy per second wasted due to resistive forces + the gain of kinetic energy per second

28
Q

What is the equation for the output power of a machine?

A

P = Fv

F = output force of the machine
v = speed of the object

29
Q

What is the definition of useful energy?

A

Energy transferred for the desired purpose

30
Q

What is the equation for the efficiency of a machine?

A

Efficiency = useful energy transferred by the machine OR work done by the machine/energy supplied to the machine

31
Q

What is a more efficient bulb than a filament light bulb?

A

Fluorescent lamp

32
Q

What are three sources of renewable energy?

A
  • Wind power - wind turbines
  • Water power - tidal power station generates hydroelectricity
  • Solar power - solar panels

physics a - level (24 decks)

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