Problem Solving Strategies

sammy gerbil

01:27

@Koolman The substitution x=e^y followed by integration by parts gives I(n)=-2nI(n-1) and it is easy to show that I(0)=2.

Kunal Pawar

01:38

How to rank the van der Waals forces according to their strength? I mean what's the order. Many books say one thing while the guy at chemguide.co.uk says something else...

Anonymous

02:01

@KunalPawar Which van der waal forces ?

Kunal Pawar

02:29

London forces, dipole-dipole and dipole induced dipole

@blue

Anonymous

@KunalPawar Dipole-dipole > Dipole induced dipole > London dispersion forces

Anonymous

London dispersion forces are due to temporary charges...so they are the weakest

Kunal Pawar

Actually it's the other way according to chemguide.co.uk and he has data to support it.

Anonymous

@KunalPawar Not possible....link?

Kunal Pawar

@blue Yeah I'll send the link wait.

chemguide.co.uk/atoms/bonding/vdwstrengths.html#top

So that's why I wanted to ask.

What option should I choose if such question comes up.

There is an exception of course, for water and alcohols I believe.

Anonymous

02:38

@KunalPawar You are interpreting the page wrongly. The main point of the page is "For most molecules, including those which can hydrogen bond, dispersion forces contribute the most to the overall intermolecular bonding That does not mean they are the strongest kind of forces.

Anonymous

By the way, why not derive the equations ?

Anonymous

Find the force between two dipoles as a function of $r$

Anonymous

You will mathematically find it to be greater than force between a dipole and a temporary induced charge

Kunal Pawar

Ah okay. Contribution not strength.

Thanks @blue

Anonymous

@KunalPawar No problem :)

Anonymous

02:47

Are you class 12?

Anonymous

Giving jee this year?

Kunal Pawar

Yeah I'm in twelfth

Yes, if I clear Mains lol.

@blue

Anonymous

How much are you getting in mains?

Anonymous

@KunalPawar

Kunal Pawar

Not a clue:/

Anonymous

02:51

Really? :P

Anonymous

Answer keys are out

Anonymous

And you have got the omr uploaded on the site :)

Kunal Pawar

Didn't dare to open them. Just waiting for them to announce the result :|

Anonymous

:P

Anonymous

Don't worry

Kunal Pawar

02:52

How much are you getting -.-

Anonymous

Around 240..

Kunal Pawar

Well halve that. And lo! You have my score -.-

Anonymous

Well, even then you should qualify for advanced

Anonymous

Cutoff is around 100

Kunal Pawar

Yeah... but it isn't like Advanced is something which is super easy. BITS seems in my reach though.

Anonymous

02:58

Anyhow, all the best :)

Kunal Pawar

Same to you...

Yashas

@blue No. It just falls over r much faster.

If I remember correctly dipole-dipole forces fall over as 1/r^4

leme check

I don't remember

I have CS exam today

Anonymous

@Yashas That is exactly what I meant

Yashas

It needn't be mathematically greater

can solve for r where it inverts

Anonymous

@Yashas Yeah, I should have framed the sentence more clearly

Yashas

03:06

how much did you get in math? :3

Anonymous

@Yashas Where? Mains?

Yashas

yes

Anonymous

60+ something

Yashas

:|

there are people in my center who say physics was the hardest lol\

people scoring 90 in math and 30 in physics

Anonymous

I got 90+ in physics

Anonymous

03:07

Lol

Anonymous

It was damn easy

Yashas

I got 100

might get more

I want them give marks for that Cp Cv question -,-

Anonymous

Even I should get more...that moment of inertia question

Yashas

yea that too

too ambiguous to understand

Anonymous

Yep

Anonymous

03:09

I wasted 3-4 minutes on it

Anonymous

:/

Yashas

:O

I wasted 10 mins+

Anonymous

But you know what, CBSE won't take a hit at its rep

Anonymous

And not give bonus more than 5

Anonymous

In the whole paper

Anonymous

03:09

There were 6 wrong questions!

Yashas

I am going to drag them to the court lol

Anonymous

wtf

Yashas

wth?

6

Cp Cv

Anonymous

@Yashas We don't have money :P

Yashas

?!?!?!

moment of inertia

what else?

Anonymous

03:10

@Yashas I'm giving you the list

Anonymous

The dibal-h question

Yashas

what was wrong?

no temperature? :D

Anonymous

Nothing was specified

Yashas

We assume DIBAL-H to be at 5 degrees when not given.

Anonymous

:/ Why should we?

Yashas

03:11

We assume that there is H20 with LiAlH4

H20 is added after LiAlH4*

if you mix them, it is a disaster

Anonymous

-_- wth...they expect us to read their mind

Anonymous

@Yashas That's quite different

Yashas

what are the other Q?

Anonymous

Doppler effect for light (relativistic) is out of syllabus...so must be bonus

Yashas

o0

I think it was there in the syllabus sheet

and it isn't hard to derive either

Anonymous

03:13

@Yashas Nope

Anonymous

I checked

Anonymous

@Yashas It is hard to derive if you don't know it beforehand

Yashas

wut

I don't want bonus to be awarded to the questions which I have got correct :'( :P :D

Anonymous

The condensation polymer question had 2 answers

Yashas

o0

Nylon 6?

I got that wrong though lol

Anonymous

03:14

There were 2 options right

Yashas

what were they?

Anonymous

But in NCERT only Nylon 6 is written...

Anonymous

@Yashas Need to check..I forgot the options..there was a quora post on it

Yashas

prntscr.com/f02ls9

Anonymous

Terylene

Anonymous

03:18

Yashas

why is Bakelite wrong?

Anonymous

And nylon 6

Anonymous

Both are correct

Yashas

Even Bakelite is correct!?

You get Navolac first

that is condensiation

Anonymous

@Yashas How does it involve hydrolysis?

Yashas

03:19

then on heating, you get Bakelite

oops

hydrolysis != condensation

Anonymous

But you see...they are NCERT freaks..I doubt they will give Terylene correct :P

Yashas

why is Nylon6 correct?

caprolactum

Anonymous

@Yashas Read ncert :P

Yashas

where is water?!

Anonymous

Yashas

03:21

o0

:(

Anonymous

@Yashas Even that is debatable....

Yashas

yaya

why?

Anonymous

We don't really need H2O

Anonymous

For nylon 6

Yashas

the question says "which involves a hydrolysis reaction"

it involves a hydrolysis reaction :(

Anonymous

03:22

Too much of controversy :P

Anonymous

Anyway, idc anymore

Yashas

what other questions had problems?

I got the strongest reducing agent question wrong ._.

Anonymous

quora.com/…

Anonymous

^^

Anonymous

Many are wrong

Yashas

03:24

.

"Circle having minimum area is also incorrect and stated by many institutes"

something wrong in math section :D

YAYAYAY

Anonymous

:P

Anonymous

4 marks bonus (if the shitty cbse agrees i.e.)

Yashas

:(

I WANT 50 BONUS

Anonymous

Forget it :P

Anonymous

We will get some NIT atleast

Yashas

03:26

Coaching centers set better papers than CBSE. No mistakes!

I am not going to NIT.

I could have gone last year lol

wut is the point if I join NIT this year ._.

Anonymous

@Yashas Well, that's a fall back option

Anonymous

If things go terribly wrong

Anonymous

03:49

@Yashas How to get the taylor series for cot(x) by diving cos(x) and sin(x)?

Anonymous

I'm not getting the correct result :/

Yashas

?

Anonymous

I did it with first 2 terms

Anonymous

$\frac{(1-x^2/2)}{(x-x^3/6)}$

Yashas

you can't take pi/2

or pi/4

or 0

Anonymous

03:51

@Yashas what? where?

Yashas

f(x) = f(a) + f'(a)(a - x)/1! + ...

for a

1

Q: Taylor series for $\cot x$

Hi guys could you show me how to do the expansion of the Taylor series of $\cot x $ at the point $x=0$. My idea was to use $\dfrac{\cos x}{\sin x} $ and I want to expand it to the second term because I have to find the limit of $\dfrac{x\cot x-1}{x^2}$ but when I do the expansion I get $\dfrac{1}...

Anonymous

@Yashas The third term is wrong there...

Yashas

which one?

Anonymous

It should be 1/45

Yashas

O is used to represent an infinite series

Anonymous

03:54

Oh no, they calculated only upto first 2 terms

Yashas

quora.com/What-is-the-derivation-of-the-expansion-of-cot-x

Anonymous

@Yashas Ah, that is the direct method :)

Anonymous

I'll do by that only

Anonymous

It is a bit lengthy though

Anonymous

I should actually memorize all of them

Yashas

03:56

You'll never need the expansion of cot x

Anonymous

@Yashas In limits ?

Yashas

write it as sin/cos

and take limits spearately

can you give an example?

Anonymous

@Yashas When cos is in denominator...

Anonymous

Then it becomes lengthy

Yashas

I don't think so

I have solved hundreds of limit problems

I never needed to use an expansion

even for sin and cos

it is pretty easy to get rid of sin and cos terms

Anonymous

04:01

Yeah, don't need it

Anonymous

It is just faster

Anonymous

Put in the taylor series. Cancel terms and lo! you get the answer

Anonymous

04:11

Wohoo! I've found a brilliant method to remember the inverse trigo taylor expansion!

Anonymous

0

Q: Proof:Taylor expansion of inverse trigonometric functions

I find it quite difficult to remember the Taylor expansion of inverse trigonometric functions.Actually in school we have been just taught the series (for finding limits in calculus without teaching us the proof). Can someone provide a short proof of these expansions (mainly for inverse trigonome...

taylor-expansion

Yashas

you are late

Anonymous

@Yashas wut?

Yashas

in realizing the uses of Taylor expansion

Anonymous

@Yashas :)

Anonymous

04:17

Better late than never

Yashas

I still manage to screw up JEE Main math -_-

how did I get more in chemistry than math?!

what the hell

TheDeadLegend

@Yashas. I feel u man. I feel you.

Yashas

lol

TheDeadLegend

That moment when you score 80 in chem but 40 in math :3

Yashas

the paper wasn't hard

I was in full blown panic

every question is lengthy

I did not know what to sovle

I wasted raw 15 mins in total by jumping b/w questions

Anonymous

04:20

Well, JEE actually tests temparament too :P

Yashas

If JEE Main was called JEE Advanced, I would have done better.

becaz I wouldn't have worried much about solving all the problems

It is like: it is JEE Main; need to get all right!

the goal is to solve as many questions as possible

whereas in JEE Adv, the goal is to solve whatever can be solved\

unless the person is some super geek aiming for rank 1

who scores 300/360 in JEE Adv too ._.

Anonymous

04:55

@Yashas Can you solve all the fiitjee aits mechanics questions?

Anonymous

I'm unable to do about 50 percent of them...:/ (without solutions)

Anonymous

Need to practice more mechanics

Yashas

If you give 2x or 3x time, I can solve :P

user123733

05:58

Hii

@blue do you study at fiijee

Anonymous

@user123733 Nope...I used to..but the teachers were not good...so I left

Anonymous

Only the test papers are good

user123733

@blue WHAT rank you get there

Anonymous

@user123733 Where?

Anonymous

I don't appear for aits anymore

user123733

06:02

in the test

oo

Anonymous

In class 11 I used to get within 500 all india

user123733

nice

Anonymous

I don't appear for them anymore

Anonymous

They contain lot of irrelevant stuff

Anonymous

@user123733 Where do you study?

user123733

06:03

self study

Anonymous

Me too :)

user123733

I have few Fiitjee materials

Yashas

12:54

I am going to get 2750 Rs from Resonance :P

Anonymous

@Yashas How?

Yashas

for clearing KVPY

My computer science question paper was insane

too many wrong questions

4/6 are wrong lol

*3

Anonymous

13:17

Did you challenge the answer key ? @Yashas

Yashas

JEE Main?

Anonymous

Please challenge it with the 2750 Rs you get :P

Anonymous

Yep

Anonymous

I want 30 marks bonus :P

Anonymous

But even 15 will do

Yashas

13:20

I am poor

need that 2750 to get out of negative pocket money

Anonymous

hehe :P

Anonymous

They will give it back to you

Yashas

10

A: What is the relation between angular and linear acceleration?

As you stated, the angular acceleration, tangential linear acceleration and distance between the reference point and the object are related using the following formula: $$\vec{a} = \vec{\alpha} \times \vec{r}$$ $\vec{r}$ is merely the displacement vector between your choice of reference point a...

that became a HNQ for no reason

such a stupid question

Anonymous

Layman questions become hnq

Anonymous

And that's for a reason

Anonymous

13:22

So that people all over the network visit it

Anonymous

And increase SE profit

Yashas

.....

Yashas

13:34

0

Q: Natural frequency of elements of a system

Is the natural frequency of each element of a system the same as every other element ? The table is frictionless.

homework-and-exercises newtonian-mechanics

interesting question

Anonymous

The answer is "no"

Anonymous

You can verify with the edge blocks

Anonymous

And take the other part as a system

Anonymous

Using reduced mass method

Anonymous

Similarly try it for the other edge block

Yashas

13:36

I would try to find the period of each block

and then generalize it for a system of n-blocks

Anonymous

One counterexample is sufficient to disprove the statement

Yashas

but I would make a new question out of it

concept test

Anonymous

14:43

Anonymous

@Yashas Even though this compound is a beta hydroxy acid why doesn't it undergo dehydration?

Icandoahandstand99

15:44

Hii

after every long time

I am again here

can anybody help me inquestion c

Anonymous

16:04

@Icandoahandstand99 What did you try?

Anonymous

The question is vague

Anonymous

How can he possibly choose to hit bush 1 when it is given that the probability is 1/2

Icandoahandstand99

@blue I could not understand the question properly

Anonymous

@Icandoahandstand99 Neither did I. The second part of the question seems vague to me...

Anonymous

It is given that the probability of hitting bush 1 is 1/2

Anonymous

16:12

But then they ask for number of bullets he must fire on bush 1

Anonymous

wtf

Icandoahandstand99

@blue can you help me in the next subjective question

I am getting the answer as 4/10

Anonymous

@Icandoahandstand99 The question isn't visible..

Icandoahandstand99

Anonymous

Divide into cases

Anonymous

16:19

5 R + (4R 1G) + ....

Icandoahandstand99

yeah i get 4 cases

total cases 10

sammy gerbil

19:09

@Icandoahandstand99 At least one red ball must be in the green box. More balls can be switched over, but only in red-green pairs. So the number of balls in the wrong box is always odd. The maximum number in the wrong box is 6+5=11 (all in the wrong box except 1 green). There are only 2 odd numbers between 1 and 11 which are not prime. Then you only have to calculate the probabilities of these 2 cases, and add them.

Transcript for

Problem Solving Strategies