2016 | OCR A2 Advancing Physics B | G494 &amp;amp; G495 | 20th &amp;amp; 28th June

Original post by terpanter

i thought its out of 60??!!

It is out of 60 the person I replied to had made a mistake.

Reply 101

Grealish

5

Original post by NamelessPersona

I got 170 to 2 s.f.

How could the bullet velocity be 170? that would lead to a ke value of around 14.5J for a 0.001kg mass, which isn't even close to 0.2J

Reply 102

terpanter

Original post by kennz

ah ok, i didnt see that you had to compare it to C, i knew it would increase but convinced myself it was 1/4 as it had to have 4 in it :biggrin:

do we have to calculate boatsman factor? they didn't give us activation energy to temperature did they?

Reply 103

Original post by jajajaaaaa

How could the bullet velocity be 170? that would lead to a ke value of around 14.5J for a 0.001kg mass, which isn't even close to 0.2J

A lot of other people I spoke to also got around 170. Energy was lost, as you had to explain why kinetic energy was not conserved.

Reply 104

Original post by terpanter

do we have to calculate boatsman factor? they didn't give us activation energy to temperature did they?

If you are talking about the question with the helium atoms then you worked out the activation energy earlier.

Reply 105

Simonium1010

7

Original post by kennz

was there an original line?

yes original line as in the line C; the line for the original conditions before things were halved and doubled

Reply 106

farryharnworth

Original post by jajajaaaaa

How could the bullet velocity be 170? that would lead to a ke value of around 14.5J for a 0.001kg mass, which isn't even close to 0.2J

Exactly - a lot of kinetic energy is lost.

0.001kg * 170 m/s = 0.17 Ns
0.081kg * 2.1m/s = 0.17 Ns

Momentum is conserved

Reply 107

Simonium1010

7

Original post by jajajaaaaa

How could the bullet velocity be 170? that would lead to a ke value of around 14.5J for a 0.001kg mass, which isn't even close to 0.2J

that is correct - that was the case. A lot of KE was lost in the collision.

Reply 108

terpanter

Original post by kennz

ah ok, i didnt see that you had to compare it to C, i knew it would increase but convinced myself it was 1/4 as it had to have 4 in it :biggrin:

we have to calculate bolzman factor for atmosphere losing helium discuss question?
i thought they didn't give us activation energy and temperature of atmosphere?!?!
**** 3 marks gone

Reply 109

Original post by Simonium1010

average mark for an A is 41-43

So it is. I'm used to using higher boundaries in my class as my teacher would say that between 75% and 80% raw marks was an A. I still stand by my point of around 46 being an A for this paper though as it wasn't outrageously hard.

Reply 110

Simonium1010

7

Original post by NamelessPersona

So it is. I'm used to using higher boundaries in my class as my teacher would say that between 75% and 80% raw marks was an A. I still stand by my point of around 46 being an A for this paper though as it wasn't outrageously hard.

no, true. Although I'd like to think the gulf between A and A* isn't as big as usual, i.e. only like 51 for 81ums = 90%ums...

Reply 111

uk_shahj

Original post by terpanter

we have to calculate bolzman factor for atmosphere losing helium discuss question?
i thought they didn't give us activation energy and temperature of atmosphere?!?!
**** 3 marks gone

they gave you the minimum energy needed for one helium atom to escape (part a)
then they gave you the temperature for the boltzmann question you're talking about

Reply 112

CSLady

11

Original post by M12345689

did anyone get 172 for the bullet velocity?

Yes !

Posted from TSR Mobile

Reply 113

Footyrulez

Not too bad a paper tbh, found it lot more wordy than previous papers and thought the vacuum questions was a real curveball

Reply 114

terpanter

Original post by uk_shahj

they gave you the minimum energy needed for one helium atom to escape (part a)
then they gave you the temperature for the boltzmann question you're talking about

Im so sorry, can anyone please tell me what are earlier questions for bolzman/helium about? Im scared i miss a page

Reply 115

Miracle1

How did you work out the velocity of the pellet?

Reply 116

Original post by Miracle1

How did you work out the velocity of the pellet?

Although I don't remember exact numbers you use conservation of momentum:
mass*velocity of pellet = total mass*velocity of tack and pellet. Using the energy from the previous part and equating to KE you can work out the velocity of the tack and pellet, allowing you to solve for u, giving around 170 ms^(-1) to 2 s.f.

Reply 117

danthebox

OP

i thought the gradient of the line on the first question remained unchanged, as the mass was doubled, number of molecules in the box was half, but half the pressure volume doubles.

question wasn't clear about the mass.

Reply 118