work, energy, power and efficiency Flashcards

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1
Q

what is energy needed for?

A

Energy is needed to make a stationary object move, to change its shape, or to warm it up

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2
Q

examples of energy stores;

A

gravitational potential stores

kinetic energy stores

thermal energy stores

elastic energy stores

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3
Q

what are different ways energy can be transferred

A

by radiation (light), electrically, mechanically

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4
Q

what is energy measured in ?

A

joules

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5
Q

1 ____ is equal to the ______ needed to raise a 1 _____ weight through a ______ height of 1 ______

A

Energy is measured in joules (J). One joule is equal to the energy needed to raise a 1 N weight through a vertical height of 1 m.

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6
Q

what happens when energy is transferred?

A

Whenever energy is transferred, the total amount of energy after the transfer is always equal to the total amount of energy before the transfer. The total amount of energy is unchanged.

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7
Q

what is the principle of conservation of energy?

A

energy cant be created or destroyed

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8
Q

what does it mean when work is done?

A

work is done on an object when a force acting on it makes a move - energy is transferred to the object

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9
Q

what does the amount of work done depend on?

A

The amount of work done depends on the force and the distance the object moved.

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10
Q

greater the _____ or further the ______, ______ the work done

A

The greater the force or the further the distance, the greater the work done.

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11
Q

equation for work done

A

force x distance moved in direction of force (parallel)

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12
Q

unit of work done

A

joule

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13
Q

equation for work done involving an angle?

A

W = F s cos theta

-s is distance travelled
-theta is angle between direction of the force and direction of motion

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14
Q

what does area under force displacement graph represent?

A

work done

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15
Q

how to work out area under graph?

A

constant/straight line = area of shapes such as triangle/square

variable-counting squares

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16
Q

what is kinetic energy

A

energy an object has due to its motion

faster an object moves the more kinetic energy it has

17
Q

equation for kinetic energy?

A

1/2mv^2

18
Q

what is potential energy?

A

energy an object has due to its position

19
Q

equation for graviatational potential energy?

A

Mgh
mass x gfs x change in height

20
Q

how does the work done affect gravitational potential energy?

A

work done on the object increases gravitational potential energy

21
Q

what can you do with KE equation and PE equation if air resistance is negligible

A

Consider an object of mass m released above the ground.

If air resistance is negligible, the object gains speed as it falls.

Its potential energy therefore decreases and its kinetic energy increases.

After falling through a vertical height ∆𝒉, its kinetic energy is equal to its loss of potential energy:

𝟏 𝒎𝒗𝟐 = 𝒎𝒈∆𝒉

22
Q

what are the ways of transferring energy from one object to another?

A

work done ( work done by a force due to one object making other object move)

heat transfer ( heat transfer from a hot object to cold object - conduction, convection, radiation)

electromagnetic waves

23
Q

definition of power

A

rate of transfer of energy

24
Q

unit for power

A

watt

equal to energy transfer rate of 1 joule per second

25
Q

equation for power

A

energy / time or work done/time

26
Q

what is the output power of an engine called?

A

motive power

27
Q

what happens when a powered object moves at a constant velocity at a constant height?

A

When a powered object moves at a constant velocity at a constant height, the resistive forces (e.g., friction, air resistance, drag) are equal and opposite to the motive force.

28
Q

where is the work done in an engine transferred to

A

The work done by the engine is transferred into the internal energy of the surroundings by the resistive forces.

29
Q

equation for work done for a powered vehicle

A

P = F V

30
Q

what is useful energy?

A

energy transferred for a purpose

31
Q

what is wasted energy

A

not all energy supplied is transferred for intended purpose

32
Q

equation for efficiency

A

useful energy transferred by machine / energy supplied to machine

or

work done by machine/energy supplied to machine

33
Q

how can we express efficiency

A

output / input

34
Q

how can efficiency be improved?

A

how efficient a device/machine is dependent on how much useful energy/power it provides compares to the total input

rest of the energy is dissipated as heat/sound - this can be made more efficient