MEI OCR Mechanics 3 - 25/05/2016 A.M.

chemari1

2

I hadn't seen a thread abut this exam so there's that. In question 2, what was the amplitude?

Reply 1

bellacutie

2

I got 0.2 i think. What dod you get for the last 2 parts of the paper i couldnt get them at all :frown:

Reply 2

chemari1

OP

2

Original post by bellacutie

I got 0.2 i think. What dod you get for the last 2 parts of the paper i couldnt get them at all :frown:

I did the first of them, I equated the energy before the coalesce, vertically below the centre, (to equate it then to that at A) to the one (before the coalesce; we got given the speed) at A .
Equated the energy before the coalesce to the new one at A
and I got a expression with a In it so I left it cause it asked for a value of K, I don't remember if it left the motion at A if so we were meant to use N2L and find 2 expressions for the velocity which would then be replaced in the energy equation giving us an answer, but I only did till the expression, I know I got full marks for Q. 1, Q.4 all marks except for those mentioned (13 however I might get some for the energy stuff) Q2 I started the integration but I don't understand how we were meant to integrate x/2 which apparently gave k as 2 still though I will pick up some marks
Q 3 I got the first 7, then the one, didn't get the amplitude so I made it up, same as the angular frequency and found a fake speed which I hope gets me 2 marks,

I revised so much for this and we get questions with vertical elastic shm, that of the circle was mad, I didn't manage to get through to all the questions about the COM, I got an A in a mock and I've lost like 37 marks, hopefully less and hopefully

Reply 3

charliemaths1207

Did anyone else find this paper to be extremely hard? I've never seen a paper like this normally I have a good idea of what to do but for the last 2 questions I was really stuck. Here's hoping the grade boundaries are REALLY low

Reply 4

chemari1

OP

2

Original post by charliemaths1207

Did anyone else find this paper to be extremely hard? I've never seen a paper like this normally I have a good idea of what to do but for the last 2 questions I was really stuck. Here's hoping the grade boundaries are REALLY low

same man

Reply 5

Aph

22

Original post by charliemaths1207

Did anyone else find this paper to be extremely hard? I've never seen a paper like this normally I have a good idea of what to do but for the last 2 questions I was really stuck. Here's hoping the grade boundaries are REALLY low

Hated it.
I loved question 1 and 3 was okay-ish... But 2ii & III and 4i and the last part was a nightmare.

Reply 6

chemari1

OP

2

Original post by Aph

Hated it.
I loved question 1 and 3 was okay-ish... But 2ii & III and 4i and the last part was a nightmare.

what do you reckon about the boundaries?

Reply 7

Aph

22

Original post by chemari1

what do you reckon about the boundaries?

I'm hoping similar to 2014 although I recon that paper was harder than 14's

Reply 8

chemari1

OP

2

Original post by Aph

I'm hoping similar to 2014 although I recon that paper was harder than 14's

In question 3 what did you put for the amplitude and angular frequency-period?

Reply 9

Aph

22

Original post by chemari1

In question 3 what did you put for the amplitude and angular frequency-period?

Amplitude was 0.2
I can't remember anything else

Reply 10

chemari1

OP

2

Original post by Aph

Amplitude was 0.2
I can't remember anything else

I was absolutely baffled by that of the amplitude, how did you find it? I don't even know how I did get to get the right answer for the equation of motion

Reply 11

¡Muy bien!

14

Original post by chemari1

I was absolutely baffled by that of the amplitude, how did you find it? I don't even know how I did get to get the right answer for the equation of motion

The equalibrium position was x=4 because the equation of motion was a=-10 (4-x) and a=0 at the centre of oscillation (when x=4).
When x=4.2 the particle is at rest, meaning it's at the extremity of the oscillation.
So A=0.2

Reply 12

chemari1

OP

2

Original post by ¡Muy bien!

The equalibrium position was x=4 because the equation of motion was a=-10 (4-x) and a=0 at the centre of oscillation (when x=4).
When x=4.2 the particle is at rest, meaning it's at the extremity of the oscillation.
So A=0.2

did it say when the particle was at rest?