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Official OCR A G481 mechanics 20th May 2013

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Reply 380

SamBBB

Original post by RafJav

I thought it was harder:/

Stupid how easy all the mock are compared to these two exams, we have just been an unlucky year!

Reply 381

teachercol

Original post by Hawthorns

Teacher Col did you think it was a hard paper?

No - it was an easy paper that its easy to make mistakes. I've just been through it with mine and they are smacking their heads saying nooooooooooooooo.

eg converting cm^3
missing %
Not proving Ke
saying grav pe goes to ke in terminal Q
Not realising all stress/strain graphs are same for a given material and not changed by length
Not working out ration to a number
Not realising spring s are both stretched so forces are in opposire directions
Not able to do algebra on monents questiion
Multiplying by 0.3 instead of dividing on power q
etc
etc

Reply 382

Arun1323

what was the answer to the ratio question to the springs and trolleys? anyone get 25/9???

Reply 383

-bethan-

Original post by Ferrari_1996

I would say it was harder IMO.

Me too!!!

Reply 384

Joeyoh9292

Original post by teachercol

You can do it by integration.

I'm doing C4 and I wouldn't have even thought of that. If anyone did actually do that, it's mighty impressive.

Reply 385

Ferrari_1996

Original post by sohailkm96

For the output power it's just the gravitational energy gained divided by time (I think), then the input power, as the output power is 30% efficient, you can find out what 1% of the input power is then times that by 100 to get input power.

I totally failed that question then.

Reply 386

ss2012

i divided by 30 for the output but cant remember what i did for the input

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Reply 387

JustFacts

Any idea when an unofficial mark scheme will be up?

Reply 388

username964430

Original post by Ferrari_1996

Oh yeah, I've remembered a question which no-one has talked about in this thread. I wasn't sure what to do on the question where it asked for the input and output power (or something like that). What did you guys get? I hope y'all know what question I'm talking about.

What i did:
First part = mgh
Second Part = mgh/45
Third part = (mgh/2) * 0.3

Cos output power was mgh(i think), input / output * 100 = 30, so output * 0.3 = input

Reply 389

teachercol

Original post by Joeyoh9292

I'm doing C4 and I wouldn't have even thought of that. If anyone did actually do that, it's mighty impressive.

It would only be A2 students who have done Newtonian World. I show them integration methods leading to area under F/t and F/x graphs

Reply 390

Arun1323

**** sakeeeee i was so confident about doing well in that exam and then it turned out to be hard.. :frown:

((( idk how well ive done unless someone posts an unofficial mark scheme (pleaseee?)

Reply 391

teachercol

Original post by JustFacts

Any idea when an unofficial mark scheme will be up?

I've done the paper. I'll type it up and post it tomorrow.

Reply 392

Lucas96

Original post by sohailkm96

Yeah but the forces are acting in opposite directions, so it's (14 x 0.5) - (14 x 0.3)/0.8 = 3.5

One of the springs compressed and one stretched but they Beth ultimately accelerated the trolley from left to right so that's why I added them

Reply 393

Ferrari_1996

Original post by Kakashidude101

What i did:
First part = mgh
Second Part = mgh/45
Third part = (mgh/2) * 0.3

Cos output power was mgh(i think), input / output * 100 = 30, so output * 0.3 = input

I probably got the first part right because I did mgh. The other two parts I failed on.

Reply 394

teachercol

Original post by Lucas96

One of the springs compressed and one stretched but they Beth ultimately accelerated the trolley from left to right so that's why I added them

It says in bold they are both stretched.

Reply 395

Joeyoh9292

Original post by teachercol

GODDAMNIT! I've just realised I dropped at least 4 marks (converting cm^3, missing %, saying grav pe goes to ke in oil (what was the answer to that then?) leaving ratio as 25/9 (which I think will be fine - if it's right), not realising about stress/strain graphs), maybe 5-6.

Reply 396

ss2012

Surly the would bring the grade boundaries down if alot of people didn't achieve as much? Or I'm I wrong

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Reply 397

SamBBB

On the trolley spring question, i got 5.25, then changed it to 14. Did anyone get any of these answers? :confused:

Reply 398

Boy_wonder_95

Original post by Arun1323

what was the answer to the ratio question to the springs and trolleys? anyone get 25/9???

Yes!

Reply 399

MikeyP96

for the stress strain graph, i put because strain is inversely proportion to the length, if he length is doubled hen the stain is halved which would give the graph a steeper gradient, is that wrong?