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Perfect answer nivedh.

Bond length is distance between hydrogen nucleus and chlorine nucleus. But bonded eectron pair between hydrogen and chlorine does not lie totally with chlorine so that we can say that a charge of -e is at chlorine atom and +e at hydrogen atom. It is some where in between hydrogen and chlorine and that is why dipole moment is ,e*l for HCl

Ellipse is a set of point whose sum of distances from two fixed points remain constant. It is also a conic with ecentricity less then 1. Here also it will be great if you please ask some specific doubt.

Waves is generated on a string when you give a transberse motion to a part of string under tension.
When this wave is reflected from the fixed end of the string then this reflected wave interferes with orignal wave to form standing waves.
There is lot of stuff that can be told about these waves. Can you please ask a specific doubt

Here i am giving general method to solve this problem. On the disc make an ring of radius r and thickness dr.
Electric field at any point onthis ring = kQ/(r^2+a^2) and it makes an agle of cos inverse (a/sqrt(a^2+r^2)) with the normal to disc.So flux through this ring

d

= (2*pi*r*dr)*(K*Q*a)/(a²+r²)^3/2

Now integrate it from 0 to R, you will get flux through disc and hence the relation.

When a person is sitting with a jerk. His velocity in downward direction first increases and then decrease. So there is first a downward acc and then an upward acc. So apparent weight will first increase and then decrease and finally willbe equall to true weight

One question at a time
Drift velocity is drift of electron per unit time where drift is difined as position of eectron in electri field with respect to its position had there been no electric feild..
In during motion electron accelerates between collisions but it again attains zero velocity after collision. So when we are talking on time scales of collision times we assume electron to be accelerated and take drift velocity as acc*collision time.Now this velocity will be different for different electrons. It may be different even for same electron in different collisions. So on a large time scale we take average drift velocity and assume it to be constant and hence use equations of uniform motion.

Omi here also we what you are doing is applying a result directly without deriving it.

In my derivation if i had taken m1 and m2 instead of m and m i would have got omega = k(m1+m2)/(m1m2). From here we take out a direct result that when ever you have two masses m1 and m2 attached with spring of spring constant k assume that one is fixed and other has a mass of m1m2/(m1+m2) (called reduced mass) and find omega or time period directly.

And this thing should be absolutly clear to you that what i have done is derivation and what you are doing is just applying a result. It is OK to do so if you know the derivation and you are doing so just to save the time. But it is criminal to do so if you don't know how that result come. Because when it comes to applying same result in some other conditions you will have to make a decision whether you can apply it there are not. And you can do that only when you have an indepth understanding of result.

It is rotating today because it was rotating yesterday. No force it required to keep rotating a body if it is once set up in rotational motion

We can say by symetry that fied wil be parallel to plane and perpendicular to dirction of current. As sheet is infinite so field should be uniform as well. Suppose we want to find field at a point P at a distance R from sheer. We make an Ampere's loop in form of rectangle of length l and bredth 2R through P such that sheet divides it in two equall part. AB and CD of length l are parallel to sheet while BC and DA are perpendicular to it.
Applying amperes law on this loop

_{[ ]}

^{[ ]} B.ld = Bl (for AB as path is parallel to field) +0(for BC as path is perpendicular to field)+Bl (for CD as path is parallel to field) +0(for DA as path is perpendicular to field)=2BL = mu_not*i_enclosed =mu_not*lamda*l

So B= mu_not*lamda/2

Let charge q is passed in time t. So current = q/t
Force on rod= iBl=(q/t)Bl
Acc = F/m = (q/t)*Bl/m
Final velocity = Acc*t = qBl/m
Or q= mv/Bl
I am getting mv/(Bl). Please check question once because i am not sure how it can be 2mv/(Bl)

It is not given where he is moving on x= 364 from +ve y to -ve y or -ve y to positive y. But Keeru has taken the motion from negative to pisitive and has given a perfect answer.Here i would like to explain one point.
cos(theta)=140/364 comes because cot(theta) = 140/336 So cos(theta)=140/sqrt(140^2+336^2)

HI friend,
The pattern of IIT JEE 2008 is still not official. We suppose that it will have only mains with an objective type paper as it was in 2007. But there are rumors around that this time it may be a subjective paper with a prilims in december and no one has any idea about what is the truth. So wait for official decleration in this matter.
As far as marks by toppers are concerned i think they lie somewhere between 75-85 percent

The only way to find

is to give small displacement dx to the body abd find the force acting on it. This will give force constant and from that you get

. Please do not get into this buisness of getting to answers directly because what seems direct in one case may change in other. In this problem suppose total streching of dx is given to the string and left. In an inertial frame (center of mass frame is one such frame) each body is diplaced by dx/2 and force on each body is Kdx. So force constant for each body

k' = F/(dx/2) = 2k

= sqrt(2k/m)

Kinematics has nothing to do with newtons law as there we are not interested in what is causing acceleration while dynamics is all about newtons law as all the results there come from F=ma