IIT JEE , AIEEE Forum - Physics , General

mukulss

hello friends.
what i m gonna say may/may not be important to anyone but i thougt a lot to put it on goiit for last few days.

actually i think some concepts occur in each subjeats of pcm when we study,which we feel are fantastic concepts.
i hope everyone might have experiened the power of such small but strong concepts while facing a jee or aieee type exam.
is not it.
so the point is let us post those fantstic,small strong concepts here,atleast one in each post from any subject.
this i think will surely help all we goiitians.
first one from me.
i think those concepts must be less in words but more in meaning so that peple can read them fast with no efforts and even jot them down for quick review before exams.
i think brilliant people like chimanshu,spidey pratekk etc
can make fantastic contributions to this page.
rates assured from me to all posts(concepts).
let any concept be from any where but i think important that we ourselves came across it and NOT searched it.
i beleive such concepts remain in mind for a long time automaticalyy
so i hope forum experts who once prepard for 12th and competitive exams still have them.
please help us experts as ever.

kinematics:
related to graphs:

Different values of displacements in s-t graph corresponding to any given v-t graph can be calculated just by calculating areas under v-t graph.
there is no need of using equations like v = u + at, etc

mukulss

subjecrts i mean pcm

mukulss

what happened friends

siddharthsaxena

physics........

mechanics - cons of linear momentium if f(ext)=0

mukulss

thanks good

mukulss

cm on contribute.

kane

vertical distance travelled in half the time of ascend is 3/4 times the greatest height whereas during a free fall it's 1/4 times the greatest height

ridhima

well the most interesting part has been

rotational motion..... to analyse diff cases of rolling and the level of problems thus generated is simply mindcracking....but throughout this one dosent feel low rather u are spending ur brain....

cheers

ridhima

for chem i think gaseous state and atomic structure are the most popular chapters amongst students.... and they are really exciting

kane

if a body takes time t to slide down a smooth inclined plane and 'nt' to slide down a rough surface,then coefficient of friction of rough surface is given by

u(neu)=(n²-1/n²)tan theta where theta is the angle of repose of the planes

deedee

if d Sn of an ap..is=An^2 + B^n

then....d common difference is............

2* coefficient of n^2

ie 2 A......in this case..

cheers.....

sankydreams

here is a shortcut method to find hybridisation
calculate number of sigma bonds that atom is making.Add this number to the number of lone pair of electrons on that atom that are not participating in resonance.The ans gives u the hybridisation

waterdemon

Here I am giving you concepts for Circular motion.

Vertical Circle:

In these cases we consider a body of any mass say "m" tied
to a string of length L whose other end is fixed.
Now if the velocity is small then body and string execute
Oscillations.

When the Velocity is larger the body describes a complete
circle.

So now the formula that:

T_B = m(V₁²-5gL)/L

Now from here we get three conditions:
Case(I) :Condition to perform complete revolution:

Here Tension in the string at B should be greater than Zero.

i.e: V₁² - 5gL > 0
V₁² > 5gL

V₁ >

5gL
0 < @

90⁰.

case(II) :Condition of Oscillation:
If V₁ <

5gL then the particle will either Oscillate about
the lowest point A or will leave the circular path.

Let Velocity vanish at some height "h₁"
then we get:

0 = V₁²-2gh₁
h₁ = V₁²/2g.

Now Let the tension vanish at some height "h₂".
then from the equation :

T = m(V₁²+g(L-3h)/L

We get:
h₂ = V₁²+gL/3g

The condition for Oscillation is that velocity should vanish before Tension i.e: h₁ < h₂

V₁²/2g < V₁²+gL/3g

V₁² < 2gL
V₁ <

2gL

Case(III):Condition for Body to leave the circular path:
This Will Occur when the string becomes Slack.
i.e:Tension vanishes earlier than velocity.

V₁²+gL/3g < V₁²/2g

V₁²> 2gL
V₁ >

2gL
90⁰ < @ < 180⁰.

So if

2gL < V₁ <

5gL
The paticle will leave the circular path somewhere between
C and B.

Hope you all find it useful.
Rate if useful.

Cheers!!!!!!!!@@@!!!!!!!!!

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