Nik's IGCSE Physics

Wednesday, 21 September 2011

P4 IGCSE Physics Student Objectives

Dear Y11 Physicists,

Thanks to Sanyam for spotting a typo in the paper versions of Obj 4.4 of the attached. Corrected version attached.

Note that this formula is correct (gives answer as a number between 1 and 0) and the same formula x 100 is also correct (gives answer as a %)

Cheers,

Mr B

P4 IGCSE Physics Student Objectives

10 June 2011

11:20

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IGCSE Physics Student Objectives for Unit 4 - New Specification.doc Download this file

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Power questions

19 August 2011

17:30

PFY, p. 120

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Answers:

f) Power is the rate of doing work

Power (In Watts) = work done (in Joules) / time (in seconds)

g) 1 watt is the rate of working at one Joule per second

13. P = Wd/t = 1000/5 = 200W

14. P = Wd/t

Work done = force x distance = 300 x 2

P = 600/6 = 100W

15. P = Wd/t

Work done = f x d = 3000 x 10

P = 30000/4 = a) 7500W => b) 7.5kW

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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)

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)

Power = Energy / Time

Power = Work done / Time

4.14 Entrance Activity Answers

19 August 2011

17:17

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

Wednesday, 14 September 2011

CoE questions

19 August 2011

17:00

PFY p.121

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Collins, p.91

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Answers PFY p121

a) W = m x g --> W = 50 x 10 = 500N CORRECT
b) GPE = W x h --> 500 x 4 = 2000J CORRECT
c) Total E at Start = Total E at End --> 2000J = KE + 0 --> 2000J CORRECT

Answers PFY p91

a) GPE = mgh --> 35 x 10 x 30 = 10500J CORRECT
b) GPE at top = KE at bottom --> KE = 1/2 mv^2 --> v = sqr(10500/(35/2)) = 24.5 m/s CORRECT
c) There is friction from the snow and the sledge, which converts the KE into heat energy; therefore not all of the GPE is transferred to KE as that energy is 'wasted' CORRECT