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# Official OCR A G481 mechanics 20th May 2013 watch

1. Also we probally can expect to use velocity and displacement time graphs and determine the displacement! Thanks for all your inputs guys really is useful to revise over few things that have now come up? has there ever been a question on Young Modulus and explaining the experiment?
2. (Original post by Baraf)
can you say the resultant force is backwards but it is less since this horizontal component of the weight cancels some of it out, this gives a lower deceleration, and a lower deceleration means the car at the inclined plane moves faster and thus get to travel further.
Yeah as the car is decelerating and the force is being applied against the weight's component down the slope. However, the resultant force is still in the braking force's direction, it just decelerates at a lower rate. For example 3600N - (component of weight down the slope (Wsintheta)) = ma , as mass is constant it has less acceleration/deceleration.
3. (Original post by yodawg321)
For airbags I got down about accelerometer and how they work.
Also for Seatbelts (may not be right) but I put also about increases time which decreases deacceleration thus decreasing force due to F=ma

Anyone else got anymore to add on?
Totally forgot about the accelerometer Thanks!
4. Anybody got Jan 2013 markscheme, can't seem to be able to locate it.
5. (Original post by james1996p)
Also we probally can expect to use velocity and displacement time graphs and determine the displacement! Thanks for all your inputs guys really is useful to revise over few things that have now come up? has there ever been a question on Young Modulus and explaining the experiment?
Yes there has, I recently did a paper and it came up, dont remember which paper but it asked for measurements, equip used and calculations.
Measurements; Original length, diameter, extension
Equip: Metre ruler, micrometer, travelling microscope
Calc: Stress=force/area
strain=extension/orginal length
Young modulus= stress/strain
Could asl say to plot agraph of stress against strain, the gradient is young modulus.
6. (Original post by _hail)
Exactly! And then you don't even have to think about the other force. And then sometimes for part b) of the question it's like: "Now find the other force." And provided it's in equilibrium, you don't have to bother with moments again- you can just resolve vertically so if the weight W is pointing down and you have your two unknowns A and B pointing up and you've figured out A in part a) you can do W=A+B so B=W-A.
Yeah i get it, thanks for the help bro
7. yh thanks for that Majjie anything else you reckon could crop up? what about materials?
8. (Original post by james1996p)
yh thanks for that Majjie anything else you reckon could crop up? what about materials?
Im thinking the ductile/brittle/polymeric stuff might come up since I havnt seen that for a while. I think we'll have to describe what each graph shows etc, Like the elastic/plastic region and whehter it obeys hookes law.
9. can someone share notes, worked questions etc on these points.

describe and explain how
1. seat belts
2. air bags
3. crumble zone

in cars reduce impact forces on the driver in accident.

and also describe how air bags work, including triggering mechanism.
10. By the way if an object or anything is thrown upwards You would use S=Ut -1/2gt^2 right? But if it was in free fall it is just S=ut +1/2at^2
11. Yh I have seen those sorts of Questions Majjie you could be right but who knows im really worried about vector traingles as i have forgotten do we just use Pythagoras? somebody HELP!!
12. (Original post by blackstarz)
By the way if an object or anything is thrown upwards You would use S=Ut -1/2gt^2 right? But if it was in free fall it is just S=ut +1/2at^2
Is this true mate? I was wondering why sometimes i get wrong answer with that....

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13. (Original post by blackstarz)
By the way if an object or anything is thrown upwards You would use S=Ut -1/2gt^2 right? But if it was in free fall it is just S=ut +1/2at^2
Not sure but if something is decelerating then 'a' is negative therefore s=ut +1/2-at^2 so the - cancels the + out
14. (Original post by james1996p)
Yh I have seen those sorts of Questions Majjie you could be right but who knows im really worried about vector traingles as i have forgotten do we just use Pythagoras? somebody HELP!!
If they ask you to work out the resultant then yes
15. (Original post by james1996p)
Yh I have seen those sorts of Questions Majjie you could be right but who knows im really worried about vector traingles as i have forgotten do we just use Pythagoras? somebody HELP!!
You can't use Pythagoras all the time. If OCR are mean they may require us to use the SINE rule.
16. (Original post by rfka)
Not sure but if something is decelerating then 'a' is negative therefore s=ut +1/2-at^2 so the - cancels the + out
Yeah i think because if it is thrown upwards the acceleration due to gravity acts downwards opposite to its direction so if it was in freefall the acceleration due to gravity is in the direction of its travel and so it accelerates
17. (Original post by blackstarz)
By the way if an object or anything is thrown upwards You would use S=Ut -1/2gt^2 right? But if it was in free fall it is just S=ut +1/2at^2
If it was thrown upwards it's just -G so -9.81
18. (Original post by Kloe95)
If they ask you to work out the resultant then yes
Oh sorry, only use Pythagoras if you have a right angle in the vector triangle when working out the resultant!
19. How do you guys revise? all i can think of doing is doing past papers
20. what do you guys think will come up as in most likely??

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