OCR Physics A newtonian World 20/6/16 Unofficial Mark Scheme

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Quick few question if you've got the time! @teachercol

1)Would I get a mark for saying "they occur at the same time" as one of the ways that paired forces are the same?
2)For the KE and EPE graph, will I get any of the 2 marks for doing the inverted hyperbole (completely inverted from EPE, like on normal graphs) but forgetting that is must not start from 0?
3)Due to getting the graph wrong, I then obviously got the max v wrong, and then got the f wrong, but still used all the correct methods. Would I get any of the 3 marks here (ecf) from the earlier max KE error? I feel I must get 1 from the f calculation for the method, but will it have the ecf? I doubt the calculation for the max v will have an ecf though. Any thoughts? Referring to question Q3)b) in it's entirety.
4) For question 5 part b I think I just used the (correct) equation from above to show that M1 is proportional to 1/R1. I don't think I showed, but I implied, that this was the same for M2 (just seemed obvious in my head, I must've not thought it was necessary to specify something so obvious in my head). Therefore M1/M2 = (1/R1)/(1/R2) = R2/R1 as required - any of the two marks here?
5) Question 6)d I got that the temp doesn't change but I think I just mentioned that the masses are cancelled in the specific calculation - do I get 1/2 or 2/2?

Also how you feeling about grade boundaries?

Reply 101

teachercol

1) Seems Ok to me
2) Probably lose 1 mark
3) I'd expect an ecf so you'd should get the last two marks and only lose 1 for 50/80 mJ
4) I just don't know until I see the actual mark scheme. Clearly you knew what you were doing. I'd hope you get full credit,.
5) Don't see why you shouldn't get 2/2 if you say the masses cancel.

Grade boundaries?
I really don't know. It wasn't a typical paper. More mathematical than most. I think that makes it easier for the majority of students at A2. Certainly my students hate the long waffly explain questions and were relieved that there weren't any.
That would push the boundaries up.
On the other hand, the binary question wasn't straightforward - I goofed when racing through paper. I spotted the problem about radii then fell for it myself.

(edited 7 years ago)

Reply 102

apache324

Original post by anonymous_veg

^33 though. Isn't that a thousand solar masses? Doesn't that seem a bit.... Odd?

The sun is a lot smaller than lots of the stars out there, but the largest one seems to be 315 solar masses...
Ok, that doesn't make sense but I really hope 1.02*10^33 is correct

(edited 7 years ago)

Reply 103

anonymous_veg

Original post by apache324

The sun is a lot smaller than lots of the stars out there, but the largest one seems to be 315 solar masses...
Ok, that doesn't make sense but I really hope 1.02*10^33 is correct

At least we agree that it doesn't make sense hahaha

Reply 104

Firestartc

Original post by teachercol

So what would you think the minimum mark for an A would be? Around 45?

Reply 105

ComputerMaths97

I probably got around 51. Really really need that to be an A*

Thanks a ton @teachercol - from all of us! Really helps settle nerves during exams.

Reply 106

ThusSpakeAlex

@teachercol

I buggered up some questions in regards to units, getting figures like 6..e17 for mass of mars, then continued using in future formulas.

Would I get a lot of marks due to ecf? I wrote down the workings etc for the subsequent questions.

Reply 107

lai812matthew

hello would i get any marks in 2bi) if i write down 2 examples of force pairs that are newton third law pair and explain because they have same magnitude, same types of forces. and i write down 2 examples of force pairs that are not newton third law pair (wtf !) and explain some they don't have same magnitude, same types of forces etc. :frown:

Reply 108

Brokensteps

Original post by Leechayy

Ohhh okay, I think I get it now. So based off the question's context (which I don't really remember) you lead to using the equal and opposite force?

So I'm guessing I'd lose 2/3 marks then :colonhash:

Posted from TSR Mobile

The context was a fireman with a hose pointed upwards at at angle.

Yeah pretty much. Just hope we got a high grade overall. I guess theres a big gap between full marks and an A. (relatively)

Reply 109

yeoubi

About 2cii), in the unofficial mark scheme, it says R = mg + Fsin55
R was ↑, mg was ↓, and from my memory, Fsin55 was ↑; hence resolving vertically, would it not be mg = R + Fsin55?

Reply 110

apache324

Original post by yeoubi

About 2cii), in the unofficial mark scheme, it says R = mg + Fsin55
R was ↑, mg was ↓, and from my memory, Fsin55 was ↑; hence resolving vertically, would it not be mg = R + Fsin55?

The upward force Fsin55 is acting on the water. Its equal and opposite 3rd law pair is acting downwards on the fireman, so it is added to the weight.

Reply 111

calruss

Any idea if in 1 b)ii) there would be any marks for finding the speed using the graph (i.e. comparing the height of the first peak to the second)?? Seemed an alright method at the time and it gave me an answer v similar to what you get if you use speed=impulse/mass (though not exactly the same). Was there any indication in the question that the graph wasn't drawn to scale?

Reply 112

Agent47_

Original post by calruss

Probably not, as there was no units on the graph so it would be incorrect to assume that it was to scale.

Reply 113

speed1✈️✈️

Original post by Danny.L

49/60 isnt an A/B calm down son.
That's A*/100% ums territory. lmfao

Hmmm well the highest boundary for a G484 paper for an A was 47, A* was 51. I suspect this paper might have very similar boundaries. So not necessarily A* territory!

But I do hope you're right!! It would be nice if I got that :smile:

Reply 114

TheFarmerLad

Original post by speed1✈️✈️

I think you could be right. Though of course I'm praying 47 is the A* ums as that's what I think I got! Everyone seems to be saying this paper was easier than recent years which I find odd as I thought it was slightly harder hmm