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# Edexcel Mathematics: Mechanics M3 6679 01 - 17 May 2017 [Exam Discussion] watch

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HORRIBLE PAPER!!
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1. How many marks was Q6 part c?
2. (Original post by .floyd.)
How many marks was Q6 part c?

Which question is it? The string one with a horizontal force?
3. ahh ffs, i probably lost 2 marks in 2b, I misread 58.8 for 55.8. For my 6 part c i got 4.62 metres per second
4. (Original post by .floyd.)
How many marks was Q6 part c?
6 big ones
5. (Original post by m3isababe)
1a)3/4

2a)33.6
b).2

3a)4.52
b)5.42

4a)25/11 a
b)23.7

5a)show that
b)show that
c)3(ag)^0.5

6a)show that
b)38.4
c)6.53

7a)show that
b)show that
c)1.02

all same!
6. I got the com to be something like 57a/29.. idk what i did wrong

also, on 7c i added 3pi/50 to the final answer, so got 1.21 as my answer, how many marks will i have lost?
7. how did people get 1.02 for the last shm? I thought u would do -0.4=0.5cost(25/3 t ) - find t. and then find the velocity and acceleration for the time the string / slack. I messed up this paper badly I even forgot how to find the mass of a hemispherical shell.... How many method marks would i get for doing everything right but not having the right mass. I messed this paper up so badly even though it was so standard ffs
8. (Original post by Major-fury)
how did people get 1.02 for the last shm? I thought u would do -0.4=0.5cost(25/3 t ) - find t. and then find the velocity and acceleration for the time the string / slack. I messed up this paper badly I even forgot how to find the mass of a hemispherical shell.... How many method marks would i get for doing everything right but not having the right mass. I messed this paper up so badly even though it was so standard ffs
When the string B broke, there was no extension in string A and so acceleration was zero. Just needed to use v=d/t.
I'm starting to think I properly ****ed up this paper.
I think for the shell we need to do 1/2*(4pi a^2), so half the surface area of a sphere.
9. (Original post by B1g Al)
6 big ones
What was the question? I think I got 9.24 as my answer but I don't remember the question :/
10. (Original post by m3isababe)
1a)3/4

2a)33.6
b).2

3a)4.52
b)5.42

4a)25/11 a
b)23.7

5a)show that
b)show that
c)3(ag)^0.5

6a)show that
b)38.4
c)6.53

7a)show that
b)show that
c)1.02
For 6.b) I got 19.2N
The string's total length is stretched to 1m, so T=(16/0.4)*(1-0.6)=24N. Then sint = 0.8 so F=19.2
11. Okay, I've got some parting queries about that paper:
- For the question that's like "A force F is HORIZONTALLY applied to...", is the diagram view perspective a top down one? It said the points A and B were on a horizontal smooth table so this makes sense to me; I spent about 10 minutes trying to figure out if it was a trick question or not
- How many marks would I lose on the COM question if I thought the mass of the hemisphere was 4/3 * pi * r^2 assuming that the rest of it was correct? (Stupid mistake on my part)
- For the last part of the last question, I tried plugging in values for the x = a cos(wt) equation and kept on getting high values for t
- w was 3 root(5)/5 (something like that) and I took x to be 0.4 (or -0.4, can't remember)
12. (Original post by LukeB98)
When the string B broke, there was no extension in string A and so acceleration was zero. Just needed to use v=d/t.
I'm starting to think I properly ****ed up this paper.
I think for the shell we need to do 1/2*(4pi a^2), so half the surface area of a sphere.
damn I'm so retarded... Do you know how many marks I'd lose for the last part for finding v but not using v=d/t. I got everything else but didn't do that bit. for the other time. And how many marks roughly for doing the COM question like usual but messing up the Mass of a hemisphere.
13. (Original post by Major-fury)
how did people get 1.02 for the last shm? I thought u would do -0.4=0.5cost(25/3 t ) - find t. and then find the velocity and acceleration for the time the string / slack. I messed up this paper badly I even forgot how to find the mass of a hemispherical shell.... How many method marks would i get for doing everything right but not having the right mass. I messed this paper up so badly even though it was so standard ffs
The question asked for time from C to A. This comprises of the time taken for C to D, then D to A.
C to D was -0.4=0.5cos(25/3 * t), where t is around 0.29s.

For D to A, the string is slack. Since the surface is smooth, the time taken to travel from D to A is distance (1.8m) divided by the speed, which you can find using v^2 = w^2 (a^2 - x^2), with a as 0.5 and x as 0.4. The speed comes out to 2.5 m/s, so time taken for D to A is 0.72s.

Time C to A is 0.72 + 0.29 = around 1.02s
14. (Original post by .floyd.)
What was the question? I think I got 9.24 as my answer but I don't remember the question :/
It was about the particle of mass 0.3kg being released from rest, so you did EPE = KE +EPE.

However,I messed up and forgot to multiply be elastic potential energy by 2, so i've lost maybe 4 marks there.

The correct answer was 6.53 I think
15. how many marks lost for writing weight component as cos rather than sinmg ?
16. How many marks was the COM question, finding v, and the last part?
17. (Original post by va1998)
Unofficial mark scheme for today's paper?
I'll try to get hold of the paper within the next few days.
18. What was question 2? Hopefully I didn't miss it
19. (Original post by Ash8991)
Okay, I've got some parting queries about that paper:
- For the question that's like "A force F is HORIZONTALLY applied to...", is the diagram view perspective a top down one? It said the points A and B were on a horizontal smooth table so this makes sense to me; I spent about 10 minutes trying to figure out if it was a trick question or not
- How many marks would I lose on the COM question if I thought the mass of the hemisphere was 4/3 * pi * r^2 assuming that the rest of it was correct? (Stupid mistake on my part)
- For the last part of the last question, I tried plugging in values for the x = a cos(wt) equation and kept on getting high values for t
- w was 3 root(5)/5 (something like that) and I took x to be 0.4 (or -0.4, can't remember)
I did the same thing with the hemispherical shell. Used 2πa^3/3 for mass. 6 mark question. I think max 3 lost for this. And maybe 1 for the next one.
20. How many marks was 3b I think I accidentally missed it completely.

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