Year 12s: what will be the first way you research your future options? >>

This discussion is now closed.

Check out other Related discussions

Official OCR A G481 mechanics 20th May 2013

Scroll to see replies

Reply 280

OllieGCSEs

Original post by StanKing

What did everyone get for acceleration from the v-t graph?
And 2nd but last question?

If the vt graph you're referring to is the one with the ball and oil, i got around 15.2ms^-2 for the deceleration, and i don't remember the second to last question haha. For the YM, i got 1.875x10^11, and for one question i remember getting 0.338 seconds or something, and i remember getting 0.372m for the x value on the moments question

Reply 281

Hawthorns

How do you do the moments question?

Reply 282

OllieGCSEs

Original post by StanKing

And what do you all think the grade boundaries will be like?

i think the boundaries will be average, maybe 45/46 for an A

Reply 283

Hayleyfsmith

What did everyone get for what happens to the gradient of the graph of the stress-strain diagram when length of the wire is doubled?

Reply 284

seajamiet

THat moments question was weird. I expected them to divide up the lengths like usual but they just gave you the whole line. I didnt have a clue.

Reply 285

ss2012

I thought that the strain will halved so half the graph. Unsure though

Posted from TSR Mobile

Reply 286

Hawthorns

Did you have to draw a tangent to work out the deceleration, and what were he two answers for describing the motion?

Reply 287

yodawg321

I got that moment distance wrong. I got 50m lol

Reply 288

Hayleyfsmith

But extension is proportional to length so strain will be unchanged surely? And a change in length will have no impact on stress so the graph should stay the same?

Reply 289

OllieGCSEs

Original post by Hayleyfsmith

What did everyone get for what happens to the gradient of the graph of the stress-strain diagram when length of the wire is doubled?

I said the gradient stayed the same because when the length doubles, the extension for the same force will double (plus the fact that the YM of a material is independent of it's length / c.s.a) but i'm not certain

Reply 290

yodawg321

Original post by Hawthorns

Did you have to draw a tangent to work out the deceleration, and what were he two answers for describing the motion?

Yeah I drew the tangent and got around 14 acceleration

Reply 291

Hawthorns

Original post by yodawg321

Yeah I drew the tangent and got around 14 acceleration

Yea I got 13.3?

Reply 292

OllieGCSEs

Original post by Hawthorns

Did you have to draw a tangent to work out the deceleration, and what were he two answers for describing the motion?

I drew a tangent, not sure if you had to though, and I said initially the ball decelerates due to resultant force acting upwards, and then it's at terminal velocity with the resultant being 0 due to the acceleration being 0 (something along those lines)

Reply 293

ss2012

Original post by Hayleyfsmith

But extension is proportional to length so strain will be unchanged surely? And a change in length will have no impact on stress so the graph should stay the same?

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

Posted from TSR Mobile

Reply 294

Hayleyfsmith

Instead of drawing a tangent I just found average acceleration between the times of changing acceleration... i got just above 13 for the gradient is this right?

Reply 295

seajamiet

Original post by Hawthorns

Did you have to draw a tangent to work out the deceleration, and what were he two answers for describing the motion?

Yeah thats what my brother did so i think so. I completly ignored that so i got it wrong. I tried to do delta v over delta t with the curve :L

Reply 296

OllieGCSEs

Original post by Hawthorns

Yea I got 13.3?

I got around 15.2 but tbh they'll have a massive margin for error so i reckon we're all correct with anything around 12-17

Reply 297

Hawthorns

Original post by Hayleyfsmith

Instead of drawing a tangent I just found average acceleration between the times of changing acceleration... i got just above 13 for the gradient is this right?

I got 13.3 :smile:

Reply 298

OllieGCSEs

Original post by seajamiet

Yeah thats what my brother did so i think so. I completly ignored that so i got it wrong. I tried to do delta v over delta t with the curve :L

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

Reply 299

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?