PFY, p. 120
f) Work, watts, joules, time
g) joule per second
13) P= Wd/t= 1000/5= 200 watts
14) Wd= F*d= 300*2
P= Wd/t= 600/6= 100 watts
16)Wd= F*d= 3000*10= 30000
P= Wd/t = 30000/4= 7500 watts= 7.5 kilowatts
Tuesday, 20 September 2011
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)
So
Power = Energy / Time
or
Power = Work done / Time
4.14 Entrance Activity Answers
· 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
Wednesday, 14 September 2011
CoE questions
19. a) W= mg= 50*10= 500N
b) GPE= wh= 500*4= 2000 J
c) GPE=KE=2000 J 3. a) GPE= mgh= 30*35*10=10500 J
b) KE= GPE
10500= 0.5mv2
v2= 600
v=24.5 m/s c) Not all of the GPE is transferred to KE because some energy is wasted due to friction.
b) GPE= wh= 500*4= 2000 J
c) GPE=KE=2000 J 3. a) GPE= mgh= 30*35*10=10500 J
b) KE= GPE
10500= 0.5mv2
v2= 600
v=24.5 m/s c) Not all of the GPE is transferred to KE because some energy is wasted due to friction.
4.13
· 4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work 
Wednesday, 7 September 2011
4.10
· 4.10 understand that work done is equal to energy transferred
PFY p.112
Collins p. 91
1. a) joules, force, distance
b) newton, meter, force
d) energy
2. Wd= F*d
Wd= 5*2=10J
4.a) Wd= F*d
Wd= 500*40= 2 kJ
b) Chemical energy from food
GPE as she walks up
1. a) W= m*g= 400*10= 4000N
Wd= F*d
50000= 4000N*d
d= 12.5m
Tuesday, 6 September 2011
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