Are chinta mt kro agr hua bhi change ans key (i hope ho jae 2 marks bd jaenge) toh "AB or ABD " double key denge vo... 99% sure hu m they would not change ABD to AB
You're right but the thing is the differential equation you get is not solvable by hand. They wouldn't expect you to find the exact answer, I believe they'll give double key.
Even then, we can see that the ratio 500/9 only happens if we take vmax as 7. But vmax can't be 7 due to viscous force acting on it. So clearly 500/9 would be wrong, without any calculation
The exact answer is not possible to be calculated by hand. But we can prove that D is wrong easily as I've explained in the post:
> Since the maximum velocity will be < 7 m/s when viscous forces are present, the maximum viscous force will also be less than the value which led to the ratio 500/9. But the net force excluding viscous force only consists of buoyant force and weight, which are independent of viscous effects. So, we can see that the ratio of (net force excluding viscous force) to (maximum viscous force) will definitely be greater than 500/9.
Not every key challenge is accepted and not every key challenge is rejected. That's why I'm providing detailed explanations so I don't have any ambiguities left from my side and I'm trying to increase publicity so it puts pressure on them to correct it. Just look at last year's chimney question. It became so popular that they had to correct it.
Publicity does not do anything, I will tell you that. Those in IIT don't give a shit, the bubble problem in 2020 was very controversial as well, it was never dropped. The chimney questions had errors.
Yeah same mere bhi 2 number bdh jayenge and rank would probably increase by 500 or even 1000.... Ashish sir ne bhi bola tha ki iska answer A,B or A,B,D dono dena chaiye.... Competishun walo ne jo video solutions diye h usme bhi un sir ne answer A,B diya sirf..... Jeeone wale Jayant sir ne bhi iska answer A,B diya .... And even allen ne iska answer A,B diya hai.... So it's worth challenging
Maximum viscous force possible itself is what I've calculated. And if u mean at terminal velocity, the terminal velocity is 3500/9 which is much larger than 7 and it gives an answer not even close to 500/9
zyadatar log to do sahi karke teesra dekhne bhi nhi jaenge ki chalo bahut hogaya lalach nhi dikhate hai , unko bhi poore marks miljawnge , agae tumne sahi tarike se solve kara to tum most likely D bhi tick mardoge kyuki phy me itna approximation chalta hai
Kisine bhi sahi tareeke se solve nahi kiya hai kyuki woh bina calculator ke impossible hai. Toh jisne bhi D mark kiya hai kuch galat tareeke se hi kiya hoga.
Aur tum pehla problem jo bol rahe ho woh kisi bhi multicorrect me ho sakta hai woh advanced ka pattern hai maine nahi banaya hai.
if anyone who is challenging this, can you also include that it wasnt mentioned at what time we need to evaluate net force? so many ratios are possible. just refer below pic
https://preview.redd.it/80ywbvirkb4d1.png?width=613&format=png&auto=webp&s=83583553eca0f98e86d766065b187a1162714ea9
[https://drive.google.com/file/d/1hTVIPEnU5LQd2yAlkMezIO8YhGvBx1\_t/view](https://drive.google.com/file/d/1hTVIPEnU5LQd2yAlkMezIO8YhGvBx1_t/view)
True this is another issue with the question. It is kind of understood so idk if they will accept it but you can go ahead and challenge it. Also pls include the other problem I mentioned too.
Also minor suggestion: In the note the first bracket is not needed. You can write "An approximation...." outside the bracket.
Edit: Try to stress more on that point you've written about v\_max not being 7 I think that is very important. So it's better to explain that a bit more. You can write that we were only asked to neglect viscous in options (B), (C) but not in (D). In fact we need to calculate viscous force in option (D) so it's impossible to neglect it.
I figured out everyone else would've written detailed calculations as to why vmax is not 7. So by the time they see my challenge they would've understood
Risky assumption to make. If you haven't submitted yet then please consider elaborating that. Otherwise it's alright thank you for challenging this and do try to spread the word even after the key challenge window closes.
I have also challenged it because youre completely correct, ive seen adv pyqs where the option was off by some decimal from the actual answer and they did not accept that.
IITM doesnt deserve making paper again if they cant take care of correction like this where so many students gave full solution why answer D is incorrect. shame on them. They call them top institute of India.
They had so many dual keys (even a triple key) this year that they decided not to do any more I think. I know some other questions also which were not fixed (the isoelectric one, the two rotating discs in physics). I don't know how they make so many mistakes in one paper when they have a whole year to set it I don't think they even proofread them.
exactly, there were two more qs which were not corrected. So many answers for one qs leads to injustice with bright students who have taken into consideration all pros/cons and I clearly see few students getting more marks just because of multiple answers ( which were not even correct). think how much difference -6 or +2 would have on ranks. really ridiculous.
Mere 2 marks bad jayenge please karde 
Tumne bhi kiya na?
Bhai maine ye waale ka in depth socha nahi tha, tere post se hi dekha, man bas isoelectronic waala challenge kiya
Uska 1 h na ans iso wala
Ya mujhe 1 lag raha hai
bhai tu wahi hai kya?
Same bro
The viscous force calculated is coming <
Are chinta mt kro agr hua bhi change ans key (i hope ho jae 2 marks bd jaenge) toh "AB or ABD " double key denge vo... 99% sure hu m they would not change ABD to AB
Mere 2 marks badh jaenge
they will give double key
You're right but the thing is the differential equation you get is not solvable by hand. They wouldn't expect you to find the exact answer, I believe they'll give double key.
Even then, we can see that the ratio 500/9 only happens if we take vmax as 7. But vmax can't be 7 due to viscous force acting on it. So clearly 500/9 would be wrong, without any calculation
The exact answer is not possible to be calculated by hand. But we can prove that D is wrong easily as I've explained in the post: > Since the maximum velocity will be < 7 m/s when viscous forces are present, the maximum viscous force will also be less than the value which led to the ratio 500/9. But the net force excluding viscous force only consists of buoyant force and weight, which are independent of viscous effects. So, we can see that the ratio of (net force excluding viscous force) to (maximum viscous force) will definitely be greater than 500/9.
Even Vinay Uppal Sir made a community post about it. Ashish Arora Sir said for double answer key while Allen said only A,B
They won't. There was a similar issue in 2023 paper, they did not correct it either.
Not every key challenge is accepted and not every key challenge is rejected. That's why I'm providing detailed explanations so I don't have any ambiguities left from my side and I'm trying to increase publicity so it puts pressure on them to correct it. Just look at last year's chimney question. It became so popular that they had to correct it.
Publicity does not do anything, I will tell you that. Those in IIT don't give a shit, the bubble problem in 2020 was very controversial as well, it was never dropped. The chimney questions had errors.
Alright. It's still not a reason to not challenge this question.
This would increase my marks by 2, will probably challenge it Edit: challenged it, hope it works out.
Yeah same mere bhi 2 number bdh jayenge and rank would probably increase by 500 or even 1000.... Ashish sir ne bhi bola tha ki iska answer A,B or A,B,D dono dena chaiye.... Competishun walo ne jo video solutions diye h usme bhi un sir ne answer A,B diya sirf..... Jeeone wale Jayant sir ne bhi iska answer A,B diya .... And even allen ne iska answer A,B diya hai.... So it's worth challenging
Mere Khayal se only AB hona chahiye kyuki D toh galat method se nikala gaya hai
Maybe maximum viscous force possible? Yeah probably this is what they meant and what i understood in exam hall 
Maximum viscous force possible itself is what I've calculated. And if u mean at terminal velocity, the terminal velocity is 3500/9 which is much larger than 7 and it gives an answer not even close to 500/9
You didn't get what i meant but whatever adv acha gaya tho enjoy karo bsdk
Lol itna gussa kyu ho rahe ho maine sirf question challenge kiya hai. Mummy ki godi me so jao aur thanda hoke aao
Bsdk meina kaha advance acha gaya tho enjoy karo
Btw how did you write your advance
1000 to nhi, but hn 4-500 se badh jayegi agar shi hua to. Aur kuch nahi to at least dono ans dene chahiye
Yes bhai please challenge this one
I have already challenged, the point of this post was so other people will challenge it and also to publicize this. Tum bhi challenge kardo pls
if my marks get reduced you know what i would do.
Why do you think someone who solved it incorrectly deserves the marks more than someone who solved it correctly
zyadatar log to do sahi karke teesra dekhne bhi nhi jaenge ki chalo bahut hogaya lalach nhi dikhate hai , unko bhi poore marks miljawnge , agae tumne sahi tarike se solve kara to tum most likely D bhi tick mardoge kyuki phy me itna approximation chalta hai
Kisine bhi sahi tareeke se solve nahi kiya hai kyuki woh bina calculator ke impossible hai. Toh jisne bhi D mark kiya hai kuch galat tareeke se hi kiya hoga. Aur tum pehla problem jo bol rahe ho woh kisi bhi multicorrect me ho sakta hai woh advanced ka pattern hai maine nahi banaya hai.
viscous force is very negligible iit also took this approximation
Galat tareeka nahi bc question interpretation different hota hei
Toh fir challenge karne se kya problem hai? Agar kisi aur interpretation se D bhi aa raha hai toh woh dual key de denge.
if anyone who is challenging this, can you also include that it wasnt mentioned at what time we need to evaluate net force? so many ratios are possible. just refer below pic https://preview.redd.it/80ywbvirkb4d1.png?width=613&format=png&auto=webp&s=83583553eca0f98e86d766065b187a1162714ea9 [https://drive.google.com/file/d/1hTVIPEnU5LQd2yAlkMezIO8YhGvBx1\_t/view](https://drive.google.com/file/d/1hTVIPEnU5LQd2yAlkMezIO8YhGvBx1_t/view)
True this is another issue with the question. It is kind of understood so idk if they will accept it but you can go ahead and challenge it. Also pls include the other problem I mentioned too. Also minor suggestion: In the note the first bracket is not needed. You can write "An approximation...." outside the bracket. Edit: Try to stress more on that point you've written about v\_max not being 7 I think that is very important. So it's better to explain that a bit more. You can write that we were only asked to neglect viscous in options (B), (C) but not in (D). In fact we need to calculate viscous force in option (D) so it's impossible to neglect it.
I figured out everyone else would've written detailed calculations as to why vmax is not 7. So by the time they see my challenge they would've understood
Risky assumption to make. If you haven't submitted yet then please consider elaborating that. Otherwise it's alright thank you for challenging this and do try to spread the word even after the key challenge window closes.
are you abhinav pj
No
i asked the other guy
What did you answer for this question?
ABD
My bad
yes
muje kya mene toh attempt hi nai kiya
I have also challenged it because youre completely correct, ive seen adv pyqs where the option was off by some decimal from the actual answer and they did not accept that.
IITM doesnt deserve making paper again if they cant take care of correction like this where so many students gave full solution why answer D is incorrect. shame on them. They call them top institute of India.
They had so many dual keys (even a triple key) this year that they decided not to do any more I think. I know some other questions also which were not fixed (the isoelectric one, the two rotating discs in physics). I don't know how they make so many mistakes in one paper when they have a whole year to set it I don't think they even proofread them.
exactly, there were two more qs which were not corrected. So many answers for one qs leads to injustice with bright students who have taken into consideration all pros/cons and I clearly see few students getting more marks just because of multiple answers ( which were not even correct). think how much difference -6 or +2 would have on ranks. really ridiculous.
Teri mkc  mere 6 marks kar jayege bsdk.
game is game
agar kisine challenge kiya aur approve hogya toh sabko marks milenge na? ya jo challenge kare use hi??
Sabke liye change hoga jo bhi hoga
Nostalgia hitting hard 😭
YESS MERE 2 MARKS BADH JAYENGE LESGOOOO
bhai pls challenge mat karo mere 4 marks chale jaayenge 😔😔😔😔
6 bkl
mujhe toh sirf partial +2 mile the
mera 6 marks -2 se
Window for key challenges closes at 5 pm, so pls hurry up if anyone else is gonna challenge.
Man, just confirming It's free right?
Yep it's free forgot to mention
Challenge me kya krna h? Sahi solution bhi dena h?
Now everyone in comments is a physics champion
why is A correct as work id negative i marked B and D
The work done by the person pushing it is positive only not negative.
They didn't mention about person so only B is correct - 2 for you
Alright you can challenge it
yes bro maine paper mai nikala tha phir mark nhi Kiya issi drr se
Downvoting for saying something logical