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Official OCR A G481 mechanics 20th May 2013

Reply 300

Hawthorns

Could anyone do the moments question??

Reply 301

OllieGCSEs

10

Original post by ss2012

But the change of length will have an impact on the strain because strain is l/x and E is stress/strain

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When length doubles, then the force required to extend it x metres is halved, so i don't think the stress/strain graph would change - this would make sense since all copper materials have the same YM regardless of their length

Reply 302

Hayleyfsmith

Original post by ss2012

But the change of length will have an impact on the strain because strain is l/x and E is stress/strain

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Strain will not change as extension is proportional to length therefore Youngs modulus will not change

Reply 303

OllieGCSEs

10

Original post by Hawthorns

How do you do the moments question?

I remember doing 0.15*x = 0.32*(50-x), then solving it

Original post by yodawg321

What did people say about the forces of graph.

For the first point I said about the drag force being greater than the weight force which means it deaccelerates.

And for the second point I put about the weight and drag forces being equal which makes constant velocity.

anyone say anything like this?

I pretty much said this too

Reply 304

Hayleyfsmith

What did everyone get for the Youngs Modulus value?

Reply 305

OllieGCSEs

10

Original post by Hayleyfsmith

What did everyone get for the Youngs Modulus value?

Around 1.875x10^11?

Reply 306

seajamiet

Original post by OllieGCSEs

dv by dt is the change in velocity over the change in time which is equal to the gradient, so that would be right?..

Well i got 50ms^-2 which seems wrong to me so i dunno but i definitely did dv/dt

Reply 307

Dan_JR_12

I hated this exam so much.

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Reply 308

teenajohny777

how did you guys work out the acceleration for the trolley question?

Reply 309

teamvezon10

Original post by OllieGCSEs

dv by dt is the change in velocity over the change in time which is equal to the gradient, so that would be right?..

Oh god, I did 1/2b*h, from a to the end of the graph as I thought the area under the V/T graph represented the DE-acceleration. So it was w/e it was at point a , the area under there. So I did that wrong, great, I must of failed that paper hard; really hard.

When working out the density for the first question, wasn't it simply the mass divded by 0.w/e it was-0.w/e it was? I was told by other students that they multiplied it by a million to make it M^3 but it said cm^3 so I assumed it was simply correct to just put a decimal point infront...?

God, that was a nightmare compared to jan 2013, I was getting A's in my past papers but I seriously think I got an E on that.

Reply 310

OllieGCSEs

10

Original post by seajamiet

Well i got 50ms^-2 which seems wrong to me so i dunno but i definitely did dv/dt

You might have done this for a different section of the graph? Either way, you could be entitled to method marks for using dv/dt :smile:

Reply 311

Liberty.

10

Original post by yodawg321

Yeah I drew the tangent and got around 14 acceleration

Lets hope that's right, since I got the exact same answer!

Reply 312

seajamiet

Can i get clarification that the force constant is the same as the spring constant and therefore was k. SO in that question where it asked you to define force constant, F/x = k would be ok?

Reply 313

ss2012

8

Original post by teamvezon10

Oh god, I did 1/2b*h, from a to the end of the graph as I thought the area under the V/T graph represented the DE-acceleration. So it was w/e it was at point a , the area under there. So I did that wrong, great, I must of failed that paper hard; really hard.

When working out the density for the first question, wasn't it simply the mass divded by 0.w/e it was-0.w/e it was? I was told by other students that they multiplied it by a million to make it M^3 but it said cm^3 so I assumed it was simply correct to just put a decimal point infront...?

God, that was a nightmare compared to jan 2013, I was getting A's in my past papers but I seriously think I got an E on that.

Same all of my mocks are As but my hopes for a decent grade are destroyed

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Reply 314

Liberty.

10

Original post by teenajohny777

how did you guys work out the acceleration for the trolley question?

I used F = kx, then substituted F into a = F/m
But now I can't remember anything else I did :confused:

Reply 315

skitz241

3

i liked that paper, i answered every question pretty confidently, but i'll hold my breathe till results day

Reply 316

OllieGCSEs

10

Original post by teamvezon10

Oh god, I did 1/2b*h, from a to the end of the graph as I thought the area under the V/T graph represented the DE-acceleration. So it was w/e it was at point a , the area under there. So I did that wrong, great, I must of failed that paper hard; really hard.

When working out the density for the first question, wasn't it simply the mass divded by 0.w/e it was-0.w/e it was? I was told by other students that they multiplied it by a million to make it M^3 but it said cm^3 so I assumed it was simply correct to just put a decimal point infront...?

God, that was a nightmare compared to jan 2013, I was getting A's in my past papers but I seriously think I got an E on that.

Sorry to hear that :frown:

I'm fairly sure i messed up the density question somehow so i can't help you with that

Reply 317

OllieGCSEs

10

Original post by Liberty.

I used F = kx, then substituted F into a = F/m
But now I can't remember anything else I did :confused:

I remember using this for A and B, then finding the resultant (2.8N i think?), then using F=ma, 2.8 =0.8xa so a=3.5ms^-2, but again, i don't know if it's right