OCR MEI M3 May 2016 - Post Exam discussion

Oh my one arithmetic slip two marks dropped. Oh also @StrangeBanana how many marks for the part after that do u think i will drop cos i used thst value of k to find the change in tension.
And also i made a stupid mistake and forgot to add weight force for the shm show that sk i coulsnt get the exact show that. Will thst be like 3 marks dropped ?

16/9 here too, I went through it with two of my physics teachers and we all got 16/9

I remember the speeds of the combined particle right after the collision was:
$\frac{5}{k+1}\sqrt{\frac{ag}{3}}$

And using conservation of energy got you a (k+1)^2 = 25/9, which you solve to get 2/3.



You do, in the collision.



I'm sure it's 2/3. I think this question tripped up most people.

did the question give wherethe particles collided ? if so i missed this aghhhhh

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did the question give wherethe particles collided ? if so i missed this aghhhhh

Most further maths didn't do M3, there were 3 of us doing additional further and 1 who bravely decided on M3 instead of D1

Well done Ed.

Guys, the answer to the last question was actually 6.
I asked my teacher and shes got a Doctorate and she said no one in the class she knows of got it right.

I'll chip in

1ai) alpha = -1, beta = 1, gamma = -1
ii) 0.05 grams
bi) 17.5m
ii) 2520N

2i) Show that k = 2
ii) Show that CM is (0.625, 0)
iii) angle was 72.6 degrees

3i) Show that the diff. equation holds
ii) amplitude = 0.2m, period = 2pi/sqrt(10)
iii) velocity = 0.384ms^-1 downward

4i) cos(alpha) = 1/3
ii) Show speed is sqrt(ag/3)
iii) k = 2/3
iv) -(8/3)mg

Please add in/correct as necessary ^^



Yeah, you get -14/3 if you don't take into account that the mass has changed after the collision



Conservation of energy to get the speed of P just before collision, then conservation of momentum to get the speed of the combined mass just after the collision (in terms of k). Then conservation of energy again, because you know its speed when it gets to A. Quite an involved question!

I did the 16/9 method- do you think I will get ANY method marks at all for that

Hi, does anyone remember the actual questions or the amount of marks available for each question? Trying to work out how many I dropped. Thanks

I remember in question 4: part 3 was 9 marks and part 4 was 4 marks.
The SHM question had a 4 mark part for amplitude and time period.

I'll chip in

1ai) alpha = -1, beta = 1, gamma = -1
ii) 0.05 grams
bi) 17.5m
ii) 2520N

2i) Show that k = 2
ii) Show that CM is (0.625, 0)
iii) angle was 72.6 degrees

3i) Show that the diff. equation holds
ii) amplitude = 0.2m, period = 2pi/sqrt(10)
iii) velocity = 0.384ms^-1 downward

4i) cos(alpha) = 1/3
ii) Show speed is sqrt(ag/3)
iii) k = 2/3
iv) -(8/3)mg

Please add in/correct as necessary ^^



Yeah, you get -14/3 if you don't take into account that the mass has changed after the collision



Conservation of energy to get the speed of P just before collision, then conservation of momentum to get the speed of the combined mass just after the collision (in terms of k). Then conservation of energy again, because you know its speed when it gets to A. Quite an involved question!

Somehow I managed to get alpha = 3, beta = -1 and gamma = 1 for the first question. For some reason I always do the worst on dimensional analysis questions. I have everything else right, so hopefully that's still well into the 90s for UMS. Although I may have messed up 1 ii) as well. Can anyone remember what questions 1 i) and 1 ii) were?

There was also a question in SHM where a = -10 (x-4) and you had to say what's the value of x at the equalibrium position? Or was it in a pastpaper and I'm already mixing things up?

Guys, the answer to the last question was actually 6.
I asked my teacher and shes got a Doctorate and she said no one in the class she knows of got it right.