4.17
<<ADs and DISADs of ENERGY SOURCES-answers.docx>>
Wednesday, 21 September 2011
Tuesday, 20 September 2011
Power questions
f) Power is the rate of doing work.
Power (in Watt) = Work done (in Joules) / time (in seconds)
g) 1 watt is a rate of working of one Joule per second.
13) A girl does 1000 joules of work in 5 seconds. What power does she develop?
P = E / t = 1000J / 5s = 200 Watts
14) A man lifts a weight of 300N through a vertical height of 2m in 6 seconds. What power does he develop?
Wd = F x d
Wd = 300 x 2
Wd = 600 Joules
P = E/t
P = 600 / 6 s
P = 100 Watts
16) A crane lifts a load of 3000N through a vertical height of 10 m in 4 seconds. What is its rate of working in a) Watts b) Kilowatts?
Wd = F x d0
Wd = 3000 x 10
Wd = 30000 Joules
P = E/t
P = 30000J / 4s
P = 7500 Watts
OR
7.5 Kilowatts
Wednesday, 14 September 2011
CoE questions
I couldn't alter fonts or colours or sizes...:S a) W = m x g
= 50 x 100
= 500N
b) GPE = mgh
= 50 x 10 x 4
= 2000J
c) Total energy at start = Total energy at end
KE = 2000J Q3
a) GPE = mgh
= 35 x 10 x 30
= 10500J
b) Total energy at start = Total energy at end
KE = 1/2 x m x v x v
10500= 1/2 x 35 x v x v
v= 24.5 m/s
c) Friction and air resistance
Some of GPE turned into heat; not all trasnferred to KE
PFY p.121 [cid:image001.png@01CC72E7.51FD2C20] Collins, p.91 [cid:image002.png@01CC72E7.51FD2C20]
= 50 x 100
= 500N
b) GPE = mgh
= 50 x 10 x 4
= 2000J
c) Total energy at start = Total energy at end
KE = 2000J Q3
a) GPE = mgh
= 35 x 10 x 30
= 10500J
b) Total energy at start = Total energy at end
KE = 1/2 x m x v x v
10500= 1/2 x 35 x v x v
v= 24.5 m/s
c) Friction and air resistance
Some of GPE turned into heat; not all trasnferred to KE
PFY p.121 [cid:image001.png@01CC72E7.51FD2C20] Collins, p.91 [cid:image002.png@01CC72E7.51FD2C20]
4.13
· 4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work
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Wednesday, 7 September 2011
4.12
· 4.12 recall and use the relationship: kinetic energy = ½ × mass × speed2 KE = ½ × m × v2
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4.11
· 4.11 recall and use the relationship: gravitational potential energy = mass × g × height GPE = m × g × h
> > > Inserted from: >
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4.10
SooHyun SooHyun Lee
11P
Bangkok Patana School
________________________________________
From: Soo Hyun Lee
Sent: 07 September 2011 14:08
To: soohyunphysics@posterous.com
Subject: 4.10 ((nogallery)) · 4.10 understand that work done is equal to energy transferred PFY p.112 [cid:image001.png@01CC6D66.70900440]
1. a) The work done (measured in Joules) is equal to the force (in Newtons) mutiplied by the distance moved (in metres).
b) 1 Joule is the work done when a force of one newton moves through a distance of one metre in the direction of the force.
c) Work done = energy transferred [cid:image002.png@01CC6D66.70900440]
2. Wd = F x d
= 5N x 2 metres
= 10 Joules [cid:image003.png@01CC6D66.70900440] Wd = F x d
= 500 N x 40 m
= 20000 Joules = 20kJ ke converted to heat and gpe Collins p. 91 [cid:image004.png@01CC6D66.70900440] Wd = F x d
50000J = F x 400kg
F = 125N
w = mg
400 x 10
4000N
W = Fd
50000J = 4000 N x d
d = 12.5m 
11P
Bangkok Patana School
________________________________________
From: Soo Hyun Lee
Sent: 07 September 2011 14:08
To: soohyunphysics@posterous.com
Subject: 4.10 ((nogallery)) · 4.10 understand that work done is equal to energy transferred PFY p.112 [cid:image001.png@01CC6D66.70900440]
1. a) The work done (measured in Joules) is equal to the force (in Newtons) mutiplied by the distance moved (in metres).
b) 1 Joule is the work done when a force of one newton moves through a distance of one metre in the direction of the force.
c) Work done = energy transferred [cid:image002.png@01CC6D66.70900440]
2. Wd = F x d
= 5N x 2 metres
= 10 Joules [cid:image003.png@01CC6D66.70900440] Wd = F x d
= 500 N x 40 m
= 20000 Joules = 20kJ ke converted to heat and gpe Collins p. 91 [cid:image004.png@01CC6D66.70900440] Wd = F x d
50000J = F x 400kg
F = 125N
w = mg
400 x 10
4000N
W = Fd
50000J = 4000 N x d
d = 12.5m
4.10
· 4.10 understand that work done is equal to energy transferred PFY p.112 [cid:image001.png@01CC6D66.70900440]
1. a) The work done (measured in Joules) is equal to the force (in Newtons) mutiplied by the distance moved (in metres).
b) 1 Joule is the work done when a force of one newton moves through a distance of one metre in the direction of the force.
c) Work done = energy transferred [cid:image002.png@01CC6D66.70900440]
2. Wd = F x d
= 5N x 2 metres
= 10 Joules [cid:image003.png@01CC6D66.70900440] Wd = F x d
= 500 N x 40 m
= 20000 Joules = 20kJ Collins p. 91 [cid:image004.png@01CC6D66.70900440] Wd = F x d
50000J = F x 400kg
F = 125N 
1. a) The work done (measured in Joules) is equal to the force (in Newtons) mutiplied by the distance moved (in metres).
b) 1 Joule is the work done when a force of one newton moves through a distance of one metre in the direction of the force.
c) Work done = energy transferred [cid:image002.png@01CC6D66.70900440]
2. Wd = F x d
= 5N x 2 metres
= 10 Joules [cid:image003.png@01CC6D66.70900440] Wd = F x d
= 500 N x 40 m
= 20000 Joules = 20kJ Collins p. 91 [cid:image004.png@01CC6D66.70900440] Wd = F x d
50000J = F x 400kg
F = 125N
4.9
· 4.9 recall and use the relationship between work, force and distance moved in the direction of the force: work done = force × distance moved Wd = F × d
Starter
· Imagine pushing a king sized bed from one side of the classroom to the other
· Would it make you feel tired?
o Yup!
· Would you have to work hard to push it?
o Yup!
· What could you change so you have to do less work pushing?
o Anything that decreases the force needed (reduce friction by putting wheels on it, ice under it, etc)
o Anything that decreases the distance travelled (only push it half way!, etc)
o So the formula for work must contain force and distance
· Would it make you feel tired?
o Yup!
· Would you have to work hard to push it?
o Yup!
· What could you change so you have to do less work pushing?
o Anything that decreases the force needed (reduce friction by putting wheels on it, ice under it, etc)
o Anything that decreases the distance travelled (only push it half way!, etc)
o So the formula for work must contain force and distance
Tuesday, 6 September 2011
Plenary Answers
[cid:image001.png@01CC6D62.FF963B40]
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Thursday, 1 September 2011
Plenary Questions
PFY p.54
1) a) Thermal energy travels through the bottom of a pan by conduction.The energy is passed form one vibrating atom to the next. All metals are good conductors.
Plastics, water and air are poor conductors (good insulators). b) Convection currents can form when liquids and gases are heated. The cold fluid sinks and the hot fluid rises. c) Energy can travel through empty space by radiation rays, which can be reflected by mirrors like light rays.
Dull black surfaces are bad radiators and good absorbers. Shiny, bright surfaces are good radiators and bad absorbers. d) A vacuum flask uses silvering to cut down heat transfer by radiation and uses a vacuum to cut down heat transfer by conduction and convection.
4.8
4.8 describe how insulation is used to reduce energy transfers from buildings and the human body Task 1
· Use this interactive animations to investigate how different insulation affects the rate of cooling of hot water
> Task 2
· Use these interactive animations to find out about the energy transfers in a house
> >
Task 3
· Test your knowledge with this quiz
>
· Use this interactive animations to investigate how different insulation affects the rate of cooling of hot water
> Task 2
· Use these interactive animations to find out about the energy transfers in a house
> >
Task 3
· Test your knowledge with this quiz
>
4.7
4.7 describe the role of convection in everyday phenomena Task 1
· Try the animation
· Extension: what is happening to the particles in the air?
>
When air particles heat up, they move apart. The bottom part of the room of hot air is less dense the top part of the room.
So the hot air rises and creates a circulation, which is convection. Task 2
· Why is Lee tired after cycling to the Sea in the morning?
· Predict what will happen when Lee cycles home in the evening
> Lee is tired after cycling to the sea in the morning because of convection current.
The sun heats up the ground quickly while the sea absorbs and contains a lot of heat energy.
The heat from the ground rises and therefore, the cold air from the sea moves towards the land.
This means Lee is riding against the wind in the morning. When Lee cycles home in the evening, he will have a difficult ride home.
Since the sun is gone, the ground will cool down quickly while the sea still contains hot air.
So hot air will rise from the sea and the wind will blow towards the sea, against Lee. [cid:image001.jpg@01CC6948.F6EBEBC0] 
· Try the animation
· Extension: what is happening to the particles in the air?
>
When air particles heat up, they move apart. The bottom part of the room of hot air is less dense the top part of the room.
So the hot air rises and creates a circulation, which is convection. Task 2
· Why is Lee tired after cycling to the Sea in the morning?
· Predict what will happen when Lee cycles home in the evening
> Lee is tired after cycling to the sea in the morning because of convection current.
The sun heats up the ground quickly while the sea absorbs and contains a lot of heat energy.
The heat from the ground rises and therefore, the cold air from the sea moves towards the land.
This means Lee is riding against the wind in the morning. When Lee cycles home in the evening, he will have a difficult ride home.
Since the sun is gone, the ground will cool down quickly while the sea still contains hot air.
So hot air will rise from the sea and the wind will blow towards the sea, against Lee. [cid:image001.jpg@01CC6948.F6EBEBC0]
4.7
4.7 1. What is the most common heat transfer mechanism in solids? Conduction
2. What is the most common heat transfer mechanism in liquids and gases? Convection
3. What is the only heat transfer mechanism in a vacuum? (Infra-red) Radiation
4. Why can't conduction happen in a vacuum? There are no particles in a vacuum to transfer the vibrations
5. What happens to the space between the particles in a gas when you heat it? The space between the particles increases
6. What happens to the density of a gas when you heat it? It decreases because the space between the particles increases
7. Why can't convection happen in a solid? In a solid the particles are fixed in position and are not free to move
2. What is the most common heat transfer mechanism in liquids and gases? Convection
3. What is the only heat transfer mechanism in a vacuum? (Infra-red) Radiation
4. Why can't conduction happen in a vacuum? There are no particles in a vacuum to transfer the vibrations
5. What happens to the space between the particles in a gas when you heat it? The space between the particles increases
6. What happens to the density of a gas when you heat it? It decreases because the space between the particles increases
7. Why can't convection happen in a solid? In a solid the particles are fixed in position and are not free to move
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