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Wjec physics unit 3 2024

Thoughts

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most questions were fine except the 6-marker on kinetic/potential energies😭 (SHM was always hard to me but in the whole question of 23 i think i got at least 14--3 more marks gone bc i also got the graph wrong haha)
also my brain wasn't functioning first thing in the morning so i forgot how to prove that the total energy was 8.5x10^13 J at the start and stared at the paper for 20 minutes thinking i was doomed💀 but then i actually did the whole paper pretty smoothly and thought it went fine
i'm also glad that the comprehension question had equations so i could get some marks by actually doing more math lol
(edited 8 months ago)
Reply 2
Original post by Usernamw365
Thoughts

Surprisingly nice
Reply 3
Original post by staycyoungluv
most questions were fine except the 6-marker on kinetic/potential energies😭 (SHM was always hard to me but in the whole question of 23 i think i got at least 14--3 more marks gone bc i also got the graph wrong haha)
also my brain wasn't functioning first thing in the morning so i forgot how to prove that the total energy was 8.5x10^13 J at the start and stared at the paper for 20 minutes thinking i was doomed💀 but then i actually did the whole paper pretty smoothly and thought it went fine
i'm also glad that the comprehension question had equations so i could get some marks by actually doing more math lol

What did u get for the 6 mark energy one?
Reply 4
Original post by Usernamw365
Thoughts

Paper could’ve been a lot worse, I didn’t like the 6 marker KE/PE. The QER was nice, and same with the circular motion questions. Found the end of the 20 mark sector hard
Reply 5
Original post by Usernamw365
What did u get for the 6 mark energy one?
U ended up having that elastic potential was like 0.022j or somehting and then kinetic was 1.5x10^-4 and hence the claim was correct
Reply 6
Original post by Usernamw365
Didn't get that. Elastic potential energy is .5 x spring constant (1.46) x extension (1.5 centimetres) squared

Yeah but u had to calculate a value for X. Using ur spring constant value that you calculated in question before. U had to do F=kx and then x = 0.03(9.81)/1.46 to get a value for x. And thne use that to calculate energy. And if u think about it they wouldn’t give 6 marks for just calculating two energies and comparing. So there must of been slightly more work involved
(edited 8 months ago)
Reply 7
Original post by Usernamw365
Didn't get that. Elastic potential energy is .5 x spring constant (1.46) x extension (1.5 centimetres) squared
this is also how i did it but i got a different constant
Original post by romanfurey
U ended up having that elastic potential was like 0.022j or somehting and then kinetic was 1.5x10^-4 and hence the claim was correct
was the elastic potential mgh = (0.03)(9.81)(0.75x10^-2) to get 2.2x10^-3 j
i didn't know if i should use 1/2kx^2 or 1/2mv^2 for the kinetic energy so i used 1/2kx^2 and got smth like 4.1x10^-5 so the claim was correct
Reply 9
Original post by staycyoungluv
was the elastic potential mgh = (0.03)(9.81)(0.75x10^-2) to get 2.2x10^-3 j
i didn't know if i should use 1/2kx^2 or 1/2mv^2 for the kinetic energy so i used 1/2kx^2 and got smth like 4.1x10^-5 so the claim was correct

Incorrect on both fronts. Kinetic energy of the spring is 1/2mv^2 and then elastic potential is 1/2kx^2 but u had to calculate a value for x using ur spring constant that u had found in the question before. Elastic potential was 0.0297J and KE was 0.00015
(edited 8 months ago)
Reply 10
Original post by romanfurey
Incorrect on both fronts. Kinetic energy of the spring is 1/2mv^2 and then elastic potential is 1/2kx^2 but u had to calculate a value for x using ur spring constant that u had found in the question before. Elastic potential was 0.0297J and KE was 0.00015

See the approach that I took was using the formula for kinetic energy as 1/2* m *(Aω)^2 and 1/2*kx^2 for the elastic potential energy, where x is the Amplitude as you want the maximum for both, provides you with the maximum velocity. I got both to = each other and ngl it made sense because think of conservation of energy, both at their maximum should equal each other I mean it’s 6 marks I definitely got method marks but what I wrote was scientific facts 😭
Original post by AbzA_34
See the approach that I took was using the formula for kinetic energy as 1/2* m *(Aω)^2 and 1/2*kx^2 for the elastic potential energy, where x is the Amplitude as you want the maximum for both, provides you with the maximum velocity. I got both to = each other and ngl it made sense because think of conservation of energy, both at their maximum should equal each other I mean it’s 6 marks I definitely got method marks but what I wrote was scientific facts 😭
I get what ur saying, but it already gave u maximum velocity. So u didn’t need to use Aw. So that knowledge wasn’t even required. So there is no chance they are giving 6 marks for doing a simple calculation with KE. W simple calculation of elastic potential with given values. And then just saying claim incorrect. That would be maximum 4 marks. So there must be something else to it or another approach
Reply 12
Original post by romanfurey
I get what ur saying, but it already gave u maximum velocity. So u didn’t need to use Aw. So that knowledge wasn’t even required. So there is no chance they are giving 6 marks for doing a simple calculation with KE. W simple calculation of elastic potential with given values. And then just saying claim incorrect. That would be maximum 4 marks. So there must be something else to it or another approach

I believe my answer is wrong in terms of what they asked, because they told us to use the maximum velocity, but idk my values for energy being different wasn’t realistic simply for the fact it states “maximum” I don’t think I got the 6 marks probably 2 for the equations and 1 for my conclusion so 3 marks most likely. But tbf it does make sense for them to also be different as realistically there will be dissipative forces acting on the system and the velocity I got using was 7.5 ish which is less than their 10, and they did say it’s approximately 10 so idk it’s whatever really, how’d you find the rest of the paper?
Original post by AbzA_34
I believe my answer is wrong in terms of what they asked, because they told us to use the maximum velocity, but idk my values for energy being different wasn’t realistic simply for the fact it states “maximum” I don’t think I got the 6 marks probably 2 for the equations and 1 for my conclusion so 3 marks most likely. But tbf it does make sense for them to also be different as realistically there will be dissipative forces acting on the system and the velocity I got using was 7.5 ish which is less than their 10, and they did say it’s approximately 10 so idk it’s whatever really, how’d you find the rest of the paper?

Yeah the reason I think the claim was correct as if u think about if elastic potential will not be affected by dissipating forces, but KE will. Honestly was all round a very nice paper. No question was particularly very challenging. I thought the one about “speed to high so answer wrong is student correct” was slightly weird, but okay. The very last question of section B was weird, but I got it eventually. Decay was nice. 1st question lovely. max and min lambda was lovely. All round a brilliant paper. But it makes me scared for grade boundaries Cus I really really want an A*
Reply 14
Original post by romanfurey
Yeah the reason I think the claim was correct as if u think about if elastic potential will not be affected by dissipating forces, but KE will. Honestly was all round a very nice paper. No question was particularly very challenging. I thought the one about “speed to high so answer wrong is student correct” was slightly weird, but okay. The very last question of section B was weird, but I got it eventually. Decay was nice. 1st question lovely. max and min lambda was lovely. All round a brilliant paper. But it makes me scared for grade boundaries Cus I really really want an A*
I pray you get the A* man, also remember there’s still unit 4, and that’s typically where marks are dropped so boundaries could be low there. Ngl the speed too high one for the circular motion also stumped me, and the last question for section B, I got it at the end and before I can finish it off and convert my answer to eV, time ran out 😭 luck wasn’t there but tbf it was probably the best paper they’ve released can’t think of an nicer one, hated them all
(edited 8 months ago)
Original post by AbzA_34
I pray you get the A* man, also remember there’s still unit 4, and that’s typically where marks are dropped so boundaries could be low there. Ngl the speed too high one for the circular motion also stumped me, and the last question for section B, I got it at the end and before I can finish it off and convert my answer to eV, time ran out 😭 luck wasn’t there but tbf it was probably the best paper they’ve released can’t think of an nicer one, hated them all

For last one it was 3/2 kt wasn’t it. With k being Boltzmann and T=298K. Then the energy was ridiculously low at 10^-21. And hence it would be hard to measure
Reply 16
Original post by romanfurey
For last one it was 3/2 kt wasn’t it. With k being Boltzmann and T=298K. Then the energy was ridiculously low at 10^-21. And hence it would be hard to measure
Yeah sneaky lads at wjec, sneaking in thermal physics. But T didn’t matter as they never gave us a temperature to use, so it just had to be realistic to room temp (unless I missed it somewhere) and yeah I said it was too low so hard to measure but didn’t get the eV conversion in literally had it in my calculator ready to press equal, and time ran out
(edited 8 months ago)
Original post by AbzA_34
Yeah sneaky lads at wjec, sneaking in thermal physics. But T didn’t matter as they never gave us a temperature to use, so it just had to be realistic to room temp (unless I missed it somewhere) and yeah I said it was too low so hard to measure but didn’t get the eV conversion in literally had it in my calculator ready to press equal, and time ran out
Yeah exactly same bro. Except I forgot to convert to eV. So will get 3/4. It said room temp so that means 298K (from front of data sheet)
Reply 18
Original post by romanfurey
Yeah exactly same bro. Except I forgot to convert to eV. So will get 3/4. It said room temp so that means 298K (from front of data sheet)

I’ll be so honest, I forgot I had the formula booklet 😭 but tbf it’s fine I’m just happy to have answered everything, dropping silly marks is naturally going to happen and it’s passed now got applied and physics unit 4 and digital technology to now focus on (dreading ict it’s a clash with physics 💀💀)
Yes I knew that I did bad on the 6 marker EPE question but I got KE and I did some workings out so hopefully I get some marks. And I couldn't get the 8.5x103 at the start but I did workings out. Other than that a decent paper! IMO harder than last year but was defo doable. So glad there was no work done graph I always get those wrong haha :smile:. Onto unit 4! Plus we still have prac in the bag.

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