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# Official OCR A G481 mechanics 20th May 2013 Watch

1. (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
2. How do you do the moments question?
3. (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
4. 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?
5. 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.
6. I thought that the strain will halved so half the graph. Unsure though

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7. Did you have to draw a tangent to work out the deceleration, and what were he two answers for describing the motion?
8. I got that moment distance wrong. I got 50m lol
9. 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?
10. (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
11. (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
12. (Original post by yodawg321)
Yeah I drew the tangent and got around 14 acceleration
Yea I got 13.3?
13. (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)
14. (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

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15. 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?
16. (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
17. (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
18. (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
19. (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?..
20. 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?

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