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# AQA Physics GCSE Unit 2 2017 (16/06) unofficial mark scheme watch

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1. MARK SCHEME IS NOW FINISHED
I will not be editing the mark scheme anymore due to mixed opinions on the answers, so just take this as a rough guideline and go along with your day. Thanks to everyone who helped

Name a common fuel used in nuclear reactors:
- Uranium(235) (1 Mark)

What happens to a nucleus undergoing fission?
- The nucleus absorbs a neutron, becoming unstable which causes it to break down into two smaller nuclei, while releasing lots of energy and 3 extra neutrons in random directions. (2 Marks)

Cosmic Rays %:
- 15% (1 Mark?)

Why someone might take in larger dose of cosmic rays?
-May be outside more often that year than average OR different geographical location OR travelled more by plane

-Nuclear (power)

Why were the teachers 3 readings different?
- Different sources emit different amounts of radiation, so even a small change in location would result in a change
OR
Nuclear decay is random, so readings may fluctuate (Its most likely this one )

Rods and polarisation:

Explain using polarisation what happens to the silk and nylon rod when rubbed:
-The nylon rod has a higher polarisation than the silk, therefore its electrons are transferred to the silk (because of its weak polarisation). The nylon rod becomes positive, due to loss of electrons and the silk becomes negative due to gain. (2 or 3 Marks)

What would happen if a pvc rod was used instead of nylon?:
-silk would become positively charged instead of negatively, due to a higher polarisation. (1 Mark)

What will happen to the reading of the same charged rods?:
-Increase

Give a reason:
-The two alike charges will repel, so the rod on the scale will get a greater downwards force, which will increase the reading

Braking Distances:

Thinking distance definition:
-Distance travelled during the drivers reaction time (1 Mark)

Braking distance by lorry:
-24m (2 Marks)

Force exerted by the brakes:
- 15 000 newtons

Name one control variable for the test:
-Gradient of the runway (1 Mark)

What else can the student measure which would show braking distance?;
- Height of the weight from the ground (1 Mark)

What do the results in figure x tell you about the relationship:
-at 2n the braking distance was 80cm, and at 8n the braking distance was 20cm. As the force increases, the distance increases.

Decay:

The student concludes that the decay is beta, explain how the results from the figure support this:
-Alpha decay would have easily been stopped by 2mm of aluminium, and gamma would remain unaffected at 6mm, so the drop in counts per minute tells us this must be beta

How could the student test for alpha?:
-Use a piece of paper instead, and see if there is a difference in counts per minute. If there is, then alpha is present. (2 or 3 Marks)
OR
Use longer distances to test for change over distance, since alpha particles don't travel far

Electricity:

Voltage passing through finger to car:
-9000V (2 Marks?)

Wearing wool over any other clothing will give you a smaller charge, two reasons why not:
- The scientist hasn't considered other materials such as leather
The materials may not have been pure? (e.g 60% wool?) (2 Marks)

LEDs and things:

LED symbol:
Little skip button inside a circle. Two arrows pointing to the top right, placed above the circle. (1 Mark)

Energy transferred by the LED:
-12J (2 Marks)

Why are LED's cheaper to run?
-Halogen and filament produce a lot of heat as waste energy (1 or 2 Marks)

Explain by using ions and electrons why temperature increases resistance:
-An increase in temperature means an increase in energy. The more energy particles (ions) have the more they shake, which makes it difficult for electrons to pass by, therefore increasing the resistance (3 Marks)

Stars:

What happens at a supernova:
-The star is unstable, so explodes (1 Mark)

6 marker:
-Gasses gather up in space and begin to cluster in to the centre of their own gravity. (nebula)
Heat from pressure results in an early star formation (protostar)
Fusion begins to occur from hydrogen atoms fusing into helium nuclei, which triggers the beginning of the main sequence star.
Here it is stable for millions of years, and fuses all of its hydrogen to generate heat and light
Once hydrogen runs out, the star begins to swell and its outer layers cool off, giving it a red colour (Red Giant)
Here it fuses atoms up to iron
Once it runs out of atoms to fuse, it dispenses its outer layer of gasses and rocks (planetary nebula) into space
White dwarf -----> black dwarf (cooling) = death of the star
(6 Marks)

Scientific theory question, why accepts some but not others?: (2 Marks)
- Some theories proven wrong through investigation
Some theories seem more reasonable than others
Some theories may have insufficient evidence, or the evidence is unreliable and irrelevant

Momentum:

Explain why, using idea of momentum, the cannon moves back when it shoots the ball:
-Momentum before= momentum after. Conservation of momentum means that the cannon will move back with the same momentum as the ball, but in opposite direction (but different speed and weight) (3 Marks)

Cannon balls momentum after 0.05 seconds:
- 1000 kg m/s (3 Marks)

If you have answers to contribute, quote my post and tell me the answer, thanks

I think boundaries will be similar to last years, around:
45- A*
38- A
27- B
20- C
12- D
2. Contribute vvv
3. Hi I failed
4. (Original post by olliestevens29)
Hi I failed
You're not the only one
5. 1. Explode
2.neutron
3.Uranium(235)
4.???
Braking distance=48N
6. Uranium235 for the first question then 'neutron' for the one after
7. What did u guys get for the final 1 I got 20000
8. I got braking distance as 30N?
9. (Original post by Frost597)
I got braking distance as 30N?
Would take away 4.5 from 0.5 and times by distance
1. Explode
2.neutron
3.Uranium(235)
4.???
Braking distance=48N
I wrote form elements heavier than iron but I think explode is still a correct answer

Posted from TSR Mobile
11. (Original post by Frost597)
I got braking distance as 30N?
I don't think distance is measured in newtons
12. If I got an A in bio chem and my isa and a C in psychics what would my overall grade be?
1. Explode
2.neutron
3.Uranium(235)
4.???
Braking distance=48N
For distance I put 24 as was a triangle
14. (Original post by CDJT2000)
For distance I put 24 as was a triangle
It is a distance time graph not a speed time graph

Posted from TSR Mobile
15. The correct answer should be (4.5-0.5) x 12 because at the start the line stay stationary which is the thinking distance while after 0.5 the velocity start to decrease which therefore u know the brake is applied

Posted from TSR Mobile
16. i put 27 , you were meant to calciate the area under the graph when the line goes down
17. (Original post by omar10000000)
i put 27 , you were meant to calciate the area under the graph when the line goes down
I got 24
18. Did we have to explain star life cycle for 6 marker?
19. (Original post by Brianlee)
The correct answer should be (4.5-0.5) x 12 because at the start the line stay stationary which is the thinking distance while after 0.5 the velocity start to decrease which therefore u know the brake is applied

Posted from TSR Mobile
Not the velocity it is the y axis I forgot what it is but it is definitely not velocity

Posted from TSR Mobile
20. (Original post by olliestevens29)
What did u guys get for the final 1 I got 20000

I got that aswell but apparently its not 20,000 because we were supposed to use the acceleration equation to find out the velocity... not sure thats what my friend did too.

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