Wjec PH1 Monday 20th May 2013

OP

Original post by MukhtarA

so what exactly happens if one switch is closed to the circuit

The switches was used to change the resistance for each place. when switch was close you have to do the 1/R + 1/R thingy to find overall resistance in that part.
6ohms = total resistance when both switches were closed
Biggest power was when there was minimum resistance which is when both switches were closed. (6ohms) 12v/6 = 2
P=I^2R P=24W (max) this is what i got anyway dunno if correct

Reply 42

bradod

What did everyone get for the mean frictional force on the bobsleigh, the acceleration of the log and velocity at the start (after 5 secs)? Thanks..

And btw, the max power was 24W and the other power was 16W - using P = (V^2)/R

Reply 43

Krish4791

4

How was the paper? Do we have a general view of how it went (maybe relative to some past papers)?

Reply 44

OP

Original post by niallain

If i remember correctly, both of the switches had to be open in order to get 1.5A.

It took me 2-3 minutes of just trial and error calculations until I got 1.5A. Wasn't too hard.

I'm pretty sure that only the first one had to be closed leaving the frist part to be 6ohms + 2ohms( from 1/4 +1/2= 1/R etc...) 12/8 = 1.5A

Reply 45

OP

Original post by bradod

What did everyone get for the mean frictional force on the bobsleigh, the acceleration of the log and velocity at the start (after 5 secs)? Thanks..

And btw, the max power was 24W and the other power was 16W - using P = (V^2)/R

i cant remember the others but the acceleration is 0.69ms^-2

Reply 46

bradod

Original post by sonyeric33

i cant remember the others but the acceleration is 0.69ms^-2

Sweet, I used different sig fig, but I got 0.71 m/(s^2)

Reply 47

19aaron96

Original post by sonyeric33

i cant remember the others but the acceleration is 0.69ms^-2

Yes I got that did u get 0.6933

Reply 48

OP

Original post by Krish4791

How was the paper? Do we have a general view of how it went (maybe relative to some past papers)?

I thought the paper was singinfacantly easier than the other past papers my estimate is 63 =A 55=B 47=C 39=D 33=E

These are only my estimates though

Reply 49

OP

Other answers i remember:

Resistance length grapth, its an positive gradient but i didnt make it cross at the 0 since i took into account of resistance ohmeter +leads etc... I dunno if its correct though.
Then you had to write about using a Micrometer to measure the diameter of the wire- use to find area and then *gradient of graph to find resistivity.

E.m.f question, e.m.f was y-intercept which i got as 1.48 internal resistance was the gradient which i got as 0.8....

The question with the bobsleigh thing was the hardest for me i did a part of it wrong really annoyed xD

Tree question was simple horizonal component and verticle component. 90*9.81 - verticle component gave one of the answers. Then after that was an F=MA question overall ok

Last question about moments was really easy start if you understand moments. I got the force of the pivot as 675N which i think is correct.

Overall easy paper i hope you did well + My answers may not be correct

Reply 50

TheGreat1

2

Original post by imconfused

i feel ur pain how did it go?

i felt as comfrotable coming out as i did from the others.....which isn't very>
i was really confised with the moments. I got the dudes weight to be 485n (ish) but the next part asked for force of pivot. i initially had that as 675(again ish) but the part after that got me confused. did we have to show that the force was 675 because i wasn't getting that at all

Reply 51

imconfused

10

Original post by TheGreat1

i felt as comfrotable coming out as i did from the others.....which isn't very>
i was really confised with the moments. I got the dudes weight to be 485n (ish) but the next part asked for force of pivot. i initially had that as 675(again ish) but the part after that got me confused. did we have to show that the force was 675 because i wasn't getting that at all

well it was in equilibrium? so I think u had to take moments at q to equal '0' I cant remember my answers but I think I roughly got similar/same answers...I mucked up on the circuit eqn -.- and few of the 3mark questions...I will be over the moon with a B! b

Reply 52

What was the initial velocity

Reply 53

xRedRockerx

Despite my "I give up I give up", I actually thought the paper was amazingly easy. I messed up a couple of the parts, namely the "prove that R = 9L" or whatever that question was. The acceleration I managed to mess up too but I'm not too bothered about that, error carried forward and whatnot. The moments question was easy marks, I got the 485N/685N too or whatever they were. Overall really happy with this paper, I'm guessing it's at least over 60 for an A. Pass mark will probably be about 40%?

Reply 54

So is it follow through marks are not because I had the right methodology but did not obtain the correct answer would this affect my other questions

Reply 55

hansjohnson

3

Hi guys for the 9R one
AS R=pL/A
p is constant
L=3times greater
so volume is same they say,that means area has to go down by a factor of 3
hence R=3/(1/3)=9
Hope that makes sense
:smile:

Reply 56

OP

Original post by hansjohnson

Hi guys for the 9R one
AS R=pL/A
p is constant
L=3times greater
so volume is same they say,that means area has to go down by a factor of 3
hence R=3/(1/3)=9
Hope that makes sense
:smile:

Gj that was the only question i didnt actually understand.
Hope everyone did good =D

Reply 57

so where would you get the marks
would you get 1 mark for stating the equation
the other mark for saying r is directly proportional to l
and one mark for saying decreases by a scale factor of 3

Reply 58

OP

Original post by MukhtarA

so where would you get the marks
would you get 1 mark for stating the equation
the other mark for saying r is directly proportional to l
and one mark for saying decreases by a scale factor of 3

You are unlikely to get a mark for stating the equation.

You will get marks for:
stating Resistivity is an constant,
realising that the area will fall by scale factor fo 3
Then 1 for getting the answer
you might get one for saying r is proportional to l

But i dont know how many marks was it worth? 3/4 i thought?

Reply 59