Power

Question 1

Flashcard 1
Q: What is power in physics?
A: Power is the rate at which energy is transferred or work is done. This means it describes how quickly energy is transferred or how quickly work is carried out.

Flashcard 2
Q: What does it mean to say that power is the “rate of doing work”?
A: Saying that power is the “rate of doing work” means it describes how much work is done per second, or how much energy is transferred each second.

Flashcard 3
Q: What happens to energy when work is done on an object?
A: When work is done on an object, energy is transferred to that object.

Flashcard 4
Q: How can power be described in terms of energy transfer each second?
A: Power describes the rate at which energy is transferred, meaning how much energy is transferred each second.

Flashcard 5
Q: What does the power of a device tell you about how it transfers energy?
A: The power of a device tells you how quickly it transfers energy. The more powerful a device is, the more energy it transfers each second.

Flashcard 6
Q: What is the standard unit of power?
A: The standard unit of power is the watt, which is abbreviated as W.

Flashcard 7
Q: What does one watt represent in terms of energy transfer?
A: One watt represents an energy transfer of one joule per second.

Flashcard 8
Q: What does it mean if a device is rated at 1 watt?
A: If a device is rated at 1 watt, it means the device transfers energy at a rate of 1 joule every second.

Flashcard 9
Q: How does transferring more joules per second affect power?
A: For every extra joule of energy transferred per second, the power increases by one watt.

Flashcard 10
Q: What equation is used to calculate power using energy transferred?
A: Power can be calculated using the equation: Power = Energy transferred ÷ Time, which can be written as P = E ÷ t.

Flashcard 11
Q: What equation is used to calculate power using work done?
A: Power can also be calculated using the equation: Power = Work done ÷ Time, which can be written as P = W ÷ t.

Flashcard 12
Q: In the power equation P = E ÷ t, what does each symbol represent and what are the units?
A: In the equation P = E ÷ t:

P represents power and is measured in watts (W).

E represents energy transferred and is measured in joules (J).

t represents time and is measured in seconds (s).

Flashcard 13
Q: In the power equation P = W ÷ t, what does each symbol represent and what are the units?
A: In the equation P = W ÷ t:

P represents power and is measured in watts (W).

W represents work done and is measured in joules (J).

t represents time and is measured in seconds (s).

Flashcard 14
Q: What are the SI units used for power, energy transferred, work done, and time?
A: Power (P) is measured in watts (W).
Energy transferred (E) is measured in joules (J).
Work done (W) is measured in joules (J).
Time (t) is measured in seconds (s).

Flashcard 15
Q: Does a powerful machine necessarily exert a stronger force?
A: No. A powerful machine is not necessarily one that exerts a stronger force, although it often ends up that way. Power specifically refers to how quickly energy is transferred, not simply how large a force is applied.

Flashcard 16
Q: What actually defines a powerful machine?
A: A powerful machine is one that transfers a large amount of energy in a short space of time.

Flashcard 17
Q: How does the power of two otherwise identical cars affect a race result?
A: If two cars are identical in every way except the power of their engines, and both race the same distance along a straight track, the car with the more powerful engine will reach the finish line faster.

Flashcard 18
Q: Why does the more powerful car reach the finish line faster?
A: The more powerful car reaches the finish line faster because it transfers the same amount of energy but over a shorter time.

Flashcard 19
Q: How can comparing two devices help to understand power?
A: Comparing two devices, such as electric motors with different power ratings, helps demonstrate how power affects the rate at which energy is transferred.

Flashcard 20
Q: In an example comparing motors, what are the power ratings of the two motors being compared?
A: The example compares an 8 W motor and a 2 W motor.

Flashcard 21
Q: In the motor comparison example, what task are both motors performing?
A: Both motors are lifting a 1 kg weight up to a height of 1 metre.

Flashcard 22
Q: Which physics equation is used to calculate the energy transferred when lifting an object?
A: The gravitational potential energy equation is used:
GPE = m × g × h.

Flashcard 23
Q: What does the equation GPE = m × g × h represent?
A: The equation GPE = m × g × h calculates gravitational potential energy, which is the energy gained by an object when it is lifted to a height in a gravitational field.

Flashcard 24
Q: What do the symbols represent in the equation GPE = m × g × h?
A: In the equation:

m represents mass.

g represents gravitational field strength.

h represents height.

Flashcard 25
Q: What units are used for mass, gravitational field strength, and height in the GPE equation?
A: Mass (m) is measured in kilograms (kg).
Gravitational field strength (g) is measured in newtons per kilogram (N/kg).
Height (h) is measured in metres (m).

Flashcard 26
Q: What value is used for gravitational field strength in the example calculation?
A: The gravitational field strength used is 9.8 N/kg.

Flashcard 27
Q: How much gravitational potential energy is gained when a 1 kg mass is lifted by 1 metre?
A: Using the equation GPE = m × g × h:
GPE = 1 × 9.8 × 1 = 9.8 J.
So the mass gains 9.8 joules of gravitational potential energy.

Flashcard 28
Q: How much energy must both motors transfer to lift the mass in the example?
A: Both motors must transfer 9.8 joules of energy to lift the 1 kg mass by 1 metre.

Flashcard 29
Q: Which equation is used to calculate the time taken by each motor to lift the mass?
A: The power equation is used:
Power = Energy transferred ÷ Time, written as P = E ÷ t.

Flashcard 30
Q: How can the power equation be rearranged to calculate time?
A: The equation can be rearranged to:
Time = Energy transferred ÷ Power.

Flashcard 31
Q: How long does the 8 W motor take to lift the mass in the example?
A: Using the equation Time = Energy ÷ Power:
Time = 9.8 ÷ 8 = 1.2 seconds.

Flashcard 32
Q: How long does the 2 W motor take to lift the mass in the example?
A: Using the equation Time = Energy ÷ Power:
Time = 9.8 ÷ 2 = 4.9 seconds.

Flashcard 33
Q: Which motor lifts the mass faster in the example and why?
A: The 8 W motor lifts the mass faster because it transfers energy at a greater rate than the 2 W motor.

Flashcard 34
Q: What general rule about power can be learned from the motor comparison example?
A: If two devices lift the same weight to the same height, the one that does it faster has a higher power because it transfers energy at a faster rate.

Answer 1

Source 1: Power POWER is the RATE at which energy is being TRANSFERRED or WORK is being done. The equations for power can be written as: Power = Energy transferred / time P = E / t OR Power = Work done / time P = W / t || UNITS: Power, denoted by P, is measured in Watts (W). Energy Transferred, denoted by E, is measured in Joules (J). Work Done, denoted by W, is measured in Joules (J). Time, denoted by t, is measured in Seconds (s). One Watt is the power from an energy transfer of one Joule per second. If a device is rated at 1 Watt, it means that it transfers energy at a rate of 1 Joule per second. ||| PRACTICAL APPLICATION - EXAMPLE QUESTION: Comparing two devices, like electric motors, is a good way to understand POWER. Let’s say we have a 8W and 2W motor lifting a 1kg weight up a height of 1m: The energy transferred by the motors can be calculated using the equation for gravitational potential energy:

Gravitational potential energy (GPE) equals mass multiplied by gravitational field strength multiplied by height.

GPE = m × g × h

Where mass is measured in kilograms (kg), gravitational field strength is 9.8 N/kg, and height is measured in metres (m).

For a 1 kg mass lifted by 1 m:

GPE = 1 × 9.8 × 1 = 9.8 J

This means both motors need to transfer 9.8 joules of energy to lift the mass.

To calculate the time taken to lift the mass, the power equation is used:

Power = Energy transferred ÷ Time

P = E ÷ t

Rearranging the equation to make time the subject:

Time = Energy transferred ÷ Power

For the 8 W motor:

Time = 9.8 ÷ 8 = 1.2 s

For the 2 W motor:

Time = 9.8 ÷ 2 = 4.9 s

Therefore, the 8 W motor lifts the mass faster than the 2 W motor because it transfers energy at a greater rate. (If both devices lift the same weight to the same height, the one that does it faster has a HIGHER POWER because it TRANSFERS energy at a FASTER rate.) /////////// Source 2: Energy and power: When work is done on an object, energy is transferred. The rate at which this energy is transferred is called power (the energy transferred each second, measured in watts ). So the more powerful a device is, the more energy it will transfer each second.

Calculating power:
The equation used to calculate power is: Power = work done ÷ time taken. This is when:

power (P) is measured in watts (W)
work done (W) is measured in joules (J)
time (t) is measured in seconds (s)
One watt is equal to one joule per second (J/s). This means that for every extra joule that is transferred per second, the power increases by one watt. ////////// Source 3: Power is the ‘Rate of Doing Work’ - i.e. How Much per Second:
1) Power is the rate of energy transfer, or the rate of doing work.
2) Power is measured in watts. One watt = 1 joule of energy transferred per second.
3) You can calculate power using these equations: Power = Energy transferred / time P = E / t OR Power = Work done / time P = W / t ||| 4) A powerful machine is not necessarily one which can exert a strong force (although it usually ends up
that way). A powerful machine is one which transfers a lot of energy in a short space of time.

Take two cars that are identical in every way apart from the power of their engines.
Both cars race the same distance along a straight race track to a finish line.
The car with the more powerful engine will reach the finish line faster than the
other car - i.e. it will transfer the same amount of energy but over less time.

Question 2

Flashcard 1

Question 3

Q: What is power in physics?

Question 4

A: Power is the rate at which energy is transferred or work is done. This means it describes how quickly energy is transferred or how quickly work is carried out.

Question 5

Flashcard 2

Question 6

Q: What does it mean to say that power is the “rate of doing work”?

Question 7

A: Saying that power is the “rate of doing work” means it describes how much work is done per second

Answer 7

or how much energy is transferred each second.

Question 8

Flashcard 3

Question 9

Q: What happens to energy when work is done on an object?

Question 10

A: When work is done on an object

Answer 10

energy is transferred to that object.

Question 11

Flashcard 4

Question 12

Q: How can power be described in terms of energy transfer each second?

Question 13

A: Power describes the rate at which energy is transferred

Answer 13

meaning how much energy is transferred each second.

Question 14

Flashcard 5

Question 15

Q: What does the power of a device tell you about how it transfers energy?

Question 16

A: The power of a device tells you how quickly it transfers energy. The more powerful a device is

Answer 16

the more energy it transfers each second.

Question 17

Flashcard 6

Question 18

Q: What is the standard unit of power?

Question 19

A: The standard unit of power is the watt

Answer 19

which is abbreviated as W.

Question 20

Flashcard 7

Question 21

Q: What does one watt represent in terms of energy transfer?

Question 22

A: One watt represents an energy transfer of one joule per second.

Question 23

Flashcard 8

Question 24

Q: What does it mean if a device is rated at 1 watt?

Question 25

A: If a device is rated at 1 watt

Answer 25

it means the device transfers energy at a rate of 1 joule every second.

Question 26

Flashcard 9

Question 27

Q: How does transferring more joules per second affect power?

Question 28

A: For every extra joule of energy transferred per second

Answer 28

the power increases by one watt.

Question 29

Flashcard 10

Question 30

Q: What equation is used to calculate power using energy transferred?

Question 31

A: Power can be calculated using the equation: Power = Energy transferred ÷ Time

Answer 31

which can be written as P = E ÷ t.

Question 32

Flashcard 11

Question 33

Q: What equation is used to calculate power using work done?

Question 34

A: Power can also be calculated using the equation: Power = Work done ÷ Time

Answer 34

which can be written as P = W ÷ t.

Question 35

Flashcard 12

Question 36

Q: In the power equation P = E ÷ t

Answer 36

what does each symbol represent and what are the units?

Question 37

A: In the equation P = E ÷ t:

Question 38

P represents power and is measured in watts (W).

Question 39

E represents energy transferred and is measured in joules (J).

Question 40

t represents time and is measured in seconds (s).

Question 41

Flashcard 13

Question 42

Q: In the power equation P = W ÷ t

Answer 42

what does each symbol represent and what are the units?

Question 43

A: In the equation P = W ÷ t:

Question 44

P represents power and is measured in watts (W).

Question 45

W represents work done and is measured in joules (J).

Question 46

t represents time and is measured in seconds (s).

Question 47

Flashcard 14

Question 48

Q: What are the SI units used for power

Answer 48

energy transferred

Question 49

A: Power (P) is measured in watts (W).

Question 50

Energy transferred (E) is measured in joules (J).

Question 51

Work done (W) is measured in joules (J).

Question 52

Time (t) is measured in seconds (s).

Question 53

Flashcard 15

Question 54

Q: Does a powerful machine necessarily exert a stronger force?

Question 55

A: No. A powerful machine is not necessarily one that exerts a stronger force

Answer 55

although it often ends up that way. Power specifically refers to how quickly energy is transferred

Question 56

Flashcard 16

Question 57

Q: What actually defines a powerful machine?

Question 58

A: A powerful machine is one that transfers a large amount of energy in a short space of time.

Question 59

Flashcard 17

Question 60

Q: How does the power of two otherwise identical cars affect a race result?

Question 61

A: If two cars are identical in every way except the power of their engines

Answer 61

and both race the same distance along a straight track

Question 62

Flashcard 18

Question 63

Q: Why does the more powerful car reach the finish line faster?

Question 64

A: The more powerful car reaches the finish line faster because it transfers the same amount of energy but over a shorter time.

Question 65

Flashcard 19

Question 66

Q: How can comparing two devices help to understand power?

Question 67

A: Comparing two devices

Answer 67

such as electric motors with different power ratings

Question 68

Flashcard 20

Question 69

Q: In an example comparing motors

Answer 69

what are the power ratings of the two motors being compared?

Question 70

A: The example compares an 8 W motor and a 2 W motor.

Question 71

Flashcard 21

Question 72

Q: In the motor comparison example

Answer 72

what task are both motors performing?

Question 73

A: Both motors are lifting a 1 kg weight up to a height of 1 metre.

Question 74

Flashcard 22

Question 75

Q: Which physics equation is used to calculate the energy transferred when lifting an object?

Question 76

A: The gravitational potential energy equation is used:

Question 77

GPE = m × g × h.

Question 78

Flashcard 23

Question 79

Q: What does the equation GPE = m × g × h represent?

Question 80

A: The equation GPE = m × g × h calculates gravitational potential energy

Answer 80

which is the energy gained by an object when it is lifted to a height in a gravitational field.

Question 81

Flashcard 24

Question 82

Q: What do the symbols represent in the equation GPE = m × g × h?

Question 83

A: In the equation:

Question 84

m represents mass.

Question 85

g represents gravitational field strength.

Question 86

h represents height.

Question 87

Flashcard 25

Question 88

Q: What units are used for mass

Answer 88

gravitational field strength

Question 89

A: Mass (m) is measured in kilograms (kg).

Question 90

Gravitational field strength (g) is measured in newtons per kilogram (N/kg).

Question 91

Height (h) is measured in metres (m).

Question 92

Flashcard 26

Question 93

Q: What value is used for gravitational field strength in the example calculation?

Question 94

A: The gravitational field strength used is 9.8 N/kg.

Question 95

Flashcard 27

Question 96

Q: How much gravitational potential energy is gained when a 1 kg mass is lifted by 1 metre?

Question 97

A: Using the equation GPE = m × g × h:

Question 98

GPE = 1 × 9.8 × 1 = 9.8 J.

Question 99

So the mass gains 9.8 joules of gravitational potential energy.

Question 100

Flashcard 28

Question 101

Q: How much energy must both motors transfer to lift the mass in the example?

Question 102

A: Both motors must transfer 9.8 joules of energy to lift the 1 kg mass by 1 metre.

Question 103

Flashcard 29

Question 104

Q: Which equation is used to calculate the time taken by each motor to lift the mass?

Question 105

A: The power equation is used:

Question 106

Power = Energy transferred ÷ Time

Answer 106

written as P = E ÷ t.

Question 107

Flashcard 30

Question 108

Q: How can the power equation be rearranged to calculate time?

Question 109

A: The equation can be rearranged to:

Question 110

Time = Energy transferred ÷ Power.

Question 111

Flashcard 31

Question 112

Q: How long does the 8 W motor take to lift the mass in the example?

Question 113

A: Using the equation Time = Energy ÷ Power:

Question 114

Time = 9.8 ÷ 8 = 1.2 seconds.

Question 115

Flashcard 32

Question 116

Q: How long does the 2 W motor take to lift the mass in the example?

Question 117

A: Using the equation Time = Energy ÷ Power:

Question 118

Time = 9.8 ÷ 2 = 4.9 seconds.

Question 119

Flashcard 33

Question 120

Q: Which motor lifts the mass faster in the example and why?

Question 121

A: The 8 W motor lifts the mass faster because it transfers energy at a greater rate than the 2 W motor.

Question 122

Flashcard 34

Question 123

Q: What general rule about power can be learned from the motor comparison example?

Question 124

A: If two devices lift the same weight to the same height

Answer 124

the one that does it faster has a higher power because it transfers energy at a faster rate.