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# I cant do these 2 questions on C4 paper A3, please help. watch

1. I have attatched the paper and the answers.

Ok heres what I need help on.

5B - I have done it down to the second from last line but I dont understand how it simplifies down in terms of pi

6B - I have no idea what they are doing there. I tried making 2 simultaneuous [sp] equations but that doesnt seem to work.

Thanks.
Attached Files
2. C4 Practice Paper A3.doc (61.0 KB, 163 views)
Attached Files
4. Answers.doc (96.0 KB, 72 views)
5. anyone? lol
6. Can you tell me where you got that paper from, if there are more?
7. http://www.thestudentroom.co.uk/t124400.html

they are here.
8. Thanks a lot man
9. 5b. Just plug in the limits and note that: cos(pi)=-1 and sin(pi)=0.

6b.
When t=0, N=7*10^18:
7 * 10^18 = A e^(0) = A

When t=8, N=3*10^18:
3 * 10^17 = 7 * 10^18 . e^(-8k)
e^(8k) = 70/3
8k = ln(7/3)
k = (1/8) ln(7/3)
10. Its quite simple.
you are integrating between π and 0. so swap the x's with π and you will get:
Code:
π*( [2πsin(π) + 2cos(π) - π²cos(π)] - [2cos(0)])
π*[(0 -2 + π²) - (2)]
= π[π² -4]
ill have a look at the other one...
11. Ok 6b.
rearranging part a gives you dN = -kN dt
divide by N so you get 1/N dN = -k dt
Integrate each side with respect to what ever they are, so you get
ln N = -kt + c
do a bit of e^ to get
N = e^(-kt +c) = Ae^-kt
12. For the final question I get 1.29*10^16, anyone else get the same?
13. thanks ppl!
14. (Original post by dvs)
5b. Just plug in the limits and note that: cos(pi)=-1 and sin(pi)=0.

6b.
When t=0, N=7*10^18:
7 * 10^18 = A e^(0) = A

When t=8, N=3*10^18:
3 * 10^17 = 7 * 10^18 . e^(-8k)
e^(8k) = 70/3

8k = ln(7/3)
k = (1/8) ln(7/3)
I STILL dont get it!!! how do u do the steps in bold?
15. by dividing by 10^17 on both sides you get 3=70e^-kt
3/70=e^-kt
ln 3 - ln 70 = -kt
k = ln 70-ln 3/t

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