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A Level Physics > C5 (Work, Energy and Power) > Flashcards

C5 (Work, Energy and Power) Flashcards

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1
Q

Work done equation

A

W= force x distance moved in the direction of the force

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2
Q

What are the units for work done

A

1 Nm= 1 J

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3
Q

What is work done equal to

A 
Energy transferred 
(Energy is defined as the capacity to do work)
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4
Q

Define energy

A

The capacity for doing work
It’s a scalar quantity (magnitude no direction)
SI units- Joules

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5
Q

The energy of systems with mass can be classified as…

A

Kinetic and gravitational potential energy

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6
Q

Kinetic energy

A

Energy due to the movement of an object

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7
Q

Gravitational potential energy

A

The energy due to the position of an object in the Earth’s gravitational field

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8
Q

Name some other forms of energy

A 
Chemical
Elastic potential
Electrical potential
Nuclear 
Radiant (electromagnetic energy)
Sound 
Internal (heat or thermal)
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9
Q

Principle of conservation of energy

A

Energy can be converted from one form to another
(The total initial energy is always equal to the total final energy)

The total energy in a closed system remains constant, energy can never be created or destroyed, but can be transferred from one form to another.

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10
Q

Equation for kinetic energy

A

Ek= 1/2 mv^2

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11
Q

What is KE directly proportional to

A

The mass and square of it’s speed

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12
Q

When can we find out the gravitational potential energy

A

When an object is in a uniform gravitational field

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13
Q

Equation for gravitational potential energy

A

Ep=mgh

Where g is the acceleration of free fall

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14
Q

When is GPE gained and lost

A

When an object gets higher GPE is gained

When an object gets lower GPE is lost

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15
Q

There are many situations where KE and GPE are exchanged

Give an example

A

As an object falls

mgh=1/2mv^2

Where v is the final velocity of the object
The mass on both side cancel out

So v= √2gh
This equation is valid only if there are no resistive forces involved.

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16
Q

What’s power

Equation

A

The rate of work done

P=W/t

17
Q

What is power measured in

A

In joules pers second Js^-1 or in watts (W)

1Wis equal to one joule per second

18
Q

How can you find the power of a car from its velocity

A

P equals W over t and so P equals Fx over t, and x over t is equal to speed. Therefore P=Fv

19
Q

Expression for efficiency

A

Efficiency= useful output energy/ total input energy x 100

20
Q

Contact forces (examples):

A 
Drag (air resistance, friction, upthrust, buoyancy)
Thrust 
Tension 
Compression 
Lift
21
Q

Non contact forces

A 
Weight 
Magnetism 
Electromagnetic 
Electrostatic 
(Last three all have potential fields).
22
Q

What are the 4 fundamental forces

A

Gravitational (W=mg)
Electromagnetic/ Electrostatic
Nuclear (weak and strong)

23
Q

How can you detect changes in gravity

A

Using a gravimeter (used to map tunnelling, caves, mines and volcanic activity).

24
Q

When can we say work is done?

A

When a force acts on something and makes it move (no motion, no work).

25
Q

Equation for work done

A

W= F x change in s (displacement)

26
Q

What is energy

A

The capacity/ ability to get work done (measured in joules).

27
Q

Useful Energy

A

Only a fraction of the energy can be considered “useful energy”

28
Q

What is work time equal to in a force-distance time graph

A

The area underneath

29
Q

What is efficiency

A

Is the measure of the amount of useful energy

30
Q

Efficiency equation

A

Efficiency (%) = useful energy output divided by total energy output

Useful work done divided by total energy input

31
Q

Momentum equation

A

p= m x x

mass x velocity

32
Q

What is the rate of change of momentum of an object proportional to?

A

To the resultant force acting on the object

F directly proportional change p/ change t

33
Q

Conservation of momentum

A

The total momentum in a close system (no external forces) is equal to the total momentum after

34
Q

In elastic collisions what is conserved

A

Kinetic energy

35
Q

Equation for kinetic energy

A

1/2 mv^2

36
Q

If a constant force acts on an object, the energy transferred (kinetic energy) is equal to…

A

The work done

37
Q

Two equations for power

A

P= change W/ change t

Therefore P= F x v

A Level Physics (28 decks)

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