Unit 4 Formulae
Tell the person next to you…
· All of the formulae from this unito eg. "The formula that links Wd, F and d is…"· All of the quantities from this unito eg. "Wd = Work done"· All of the units from this unito eg. "The unit of Work Done is the Joule"Answers
Formulae
· Efficiency = Useful Eout/Total Ein x 100or Efficiency = Useful Eout/Total Ein
· Wd = F x d· GPE = mgh· KE = ½mv2· P = E/t or P = Wd/t· Total Ein = Total Eout(Principle of Conservation of Energy)
Quantities and Units
· Ein = Energy input (J)· Wd = Work done (J)· GPE = Gravitational Potential Energy (J)· KE = Kinetic Energy (J)· F = force (N)· d = distance moved in the direction of the force (m)· m = mass (kg)· g = gravitational field strength (N/kg)· gearth = 10N/kg· h = height (m)· v = velocity (m/s)· P = power (W)· t = time (s)
Monday, September 26, 2011
Do you know your formulae?
Monday, September 19, 2011
4.17 Answers
4.17 describe the advantages and disadvantages of methods of large-scale electricity production from various renewable and non-renewable resources
<<ADs and DISADs of ENERGY SOURCES-answers.docx>>
4.16
·4.16 understand the energy transfers involved in generating electricity using:· wind· water· geothermal resources· solar heating systems· solar cells· fossil fuels· nuclear power
4.17
·4.17 describe the advantages and disadvantages of methods of large-scale electricity production from various renewable and non-renewable resources
Monday, September 12, 2011
4.15
·4.15 use the relationship between power, work done (energy transferred) and time taken:power = work done P = Wd
time taken t
P = Wd / tP = E / tP = Power (Watts)Wd = Work Done (Joules)E = Energy Transferred (Joules)t = Time (s)
Power questions
PFY, p. 120
f) power is the rate of doing work.
power (in watts) = work done ( in joules) / time (in seconds)
g) 1 watt is a rate of working of one power joule per second.
13. P=E/t 1000/5= 200watts
14. P= E/t (300 x 2) / 6= 100watts
16. P= E/t (3000 x 10) / 4 = a) 7500watts
b) 7.5 kilowatts
4.14
·4.14 describe power as the rate of transfer of energy or the rate of doing work"Rate" just means "divided by time" (see Entrance Activity)SoPower = Energy / TimeorPower = Work done / Time
Entrance Activity Answers
Tell the person next to you...· You can run up the stairs in the Science block in 30 seconds.· Mr. Roff can run up the stairs in the Science block in 20 seconds.· Who is the most powerful? Why?· Mr Roff. He does more work running up the stairs (because has a higher weight) in a shorted time so he is more powerful
· It takes 2 minutes to fill the 20 litre sinks in this room with water.· How fast is the sink filling?· 10 litres/min· At what rate is the sink filling?· 10 litres/min· How long would it take to fill a 10 litre sink?· 1 min
CoE questions
PFY p.121
19
a) W = m x g 50 x 10 = 500 newtons
b) GPE= m x g x h 50 x 10 x 4 = 2000 joules
c) GPE = KE 2000 joules
Q3Collins, p.91
a) GPE= m x g x h GPE = 35 x 10 x 30 GPE= 10500 joules
b) KE = 1/2 mv^2 10500 = 1/2 x 35 x v^2 V= 24.5m/s
c) There is energy lost due to friction as heat.
4.13
·4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work
4.11
·4.11 recall and use the relationship:gravitational potential energy = mass × g × height
GPE = m × g × h
Friday, September 9, 2011
4.10
·4.10 understand that work done is equal to energy transferred
PFY p.112
1.
a) The work done (measured in joules) is equal to the force (in newtons) multiplied by the distanced 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)
d) work done= energy transferred
work done = force x distance.
work done = 5 newtons x 2 metres.
= 10J
work done = force x distance
work done = 500 newtons x 40 metres.
= 20KJ or 20000J
Collins p. 91
work done = force x distance
work done = 50000/4000
= 12.5m
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 - answers
Tell the person next to you...· 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
Monday, September 5, 2011
Plenary Questions
PFY p.54
1
a) Thermal energy travels through the bottom of a pan by convection. The energy is passed from one vibrating atom to the next. All metals are good conducts. Plastic, water and air are poor conductors (good insulators)
b) Convection currents can form when liquids and gases are heated. The cold fluid falls and the hot fluids rises.
c) Energy can travel through empty space by radiation rays, which can be reflected by mirror like light rays. Dull black surfaces are good 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 conduction and uses a vacuum to cut down heat transfer by convection and radiation.
4.8
·4.8 describe how insulation is used to reduce energy transfers from buildings and the human bodyTask 1
· Use this interactive animations to investigate how different insulation affects the rate of cooling of hot water<<Cooling of hot water with insulation - interactive.swf>>Task 2
· Use these interactive animations to find out about the energy transfers in a house
Task 3
· Test your knowledge with this quiz<<Quiz - Types of energy transfers in a house.swf>>
Saturday, September 3, 2011
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