4.16
10 June 2011
11:55
· 4.16 understand the energy transfers involved in generating electricity using:
· wind
· water
· geothermal resources
· solar heating systems
· solar cells
· fossil fuels
· nuclear power
| |||
| <<Teacher Presentation.ppt>> | <<wind energy story.swf>> |
| |||
| <<Srinakarin Hydro Dam, Kanchanaburi.avi>> | ||
| |||
|
4.14
10 June 2011
11:53
· 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)
So
Power = Energy / Time
or
Power = Work done / Time
4.15
10 June 2011
11:54
· 4.15 use the relationship between power, work done (energy transferred) and time taken:
power = work done P = Wd
time taken t
P = Wd / t
P = E / t
P = Power (Watts, W)
Wd = Work Done (Joules, J)
E = Energy Transferred (Joules, J)
t = Time (s)
PFY P 120
F) power is the rate of doing work
Power (in watts) = work done (in watts) / 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? 1000/5= 5000W
14) a man lifts a weight of 300N through a vertical height of 2m in 6 seconds. What power does he develop? 300 x 2 = 600W
16) a crane lifts a load of 3000N through a vertical height of 10m in 4 seconds. What is its rate of working in a) watts b) kilowatts
a) 3000 x 10 = 30,000W
b) 30kW
4.13
10 June 2011
11:53
· 4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work
<<CoE.ppt>>
19. a) 500N/kg
b) GPE = mgh
GPE = 50 x 10 x 4 = 2000J
c) KE = ½ m v2
KE = 0.5 x 50 x 2000 = 50000m/s2
Q3. A) GPE = mgh
GPE = 35 x 10 x 30 = 10,500J
B) KE = ½mv2
But KE (bottom) = GPE (top)
10,500 = ½ x 35 x v2
v2 = 600
v = 24.5m/s
C) because some of it got wasted by heat through friction
PFY p.121
Collins, p.91
4.10
10 June 2011
11:51
· 4.10 understand that work done is equal to energy transferred
PFY p.112
Collins p. 91
4.9
10 June 2011
11:38
· 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
|
| |||||
|
|
|
|
|
|
|
