IIT JEE , AIEEE Forum - Physics , Mechanics

karthik2007

deadline will be tomorrow night 10 pm

anchitsaini

being in eleventh is proving a major disadvantage in this test , nevertheless i'll try my best--
3--Y=2L/pie
4--b,c
6--c

karthik2007

those of you keen on mailing me the answers -

snicker.jeers@gmail.com

sidd_daga

the 6th question pleae.....couldnt bet answrere...

tarinbansal

I am getting the following answers-

1- A

2-

A(1-1/k)

Where A is the area of plate.

3-

Y=2L

4- B,C

6- B

priyesh

1) a)

2)

A(1 - 1/k)

3) 2L =piY

4) b),c)

5) h/p^2 * dU/dx

LAMPARD

1)a
2)
3)

Y=2L
4)b,c
5)2h/p² *dU/dX,where p=mv...
6)b

nitigya

my answers

1) a

2)

A(1-1/k) where a= area of plate

3) y

=2l

4)b,d

5)h/p² * du/dx

6)b

karthik2007

Okay. I think it is time to post the ranks and marks. Quite an interesting test. The people whom I expected to top seem to have made silly mistakes.

Rank 1:

Rooney - 50/50

Rank 2:

Priyesh - 40/50

Rank 3:

tarinbansal - 33/50

Rank 4:

anchitsahini - 30/50 (Amazing performance by this lad. He's just in 11th, and got ALL OF THE 11TH STD QUESTIONS HE ATTEMPTED RIGHT!!!. Its unfortunate that he couldn't attempt the rest.)

Rank 5:

Lampard - 23/50
raulrag - 23/50

Rank 6:

Feynmann - 16/50
Nitigya - 16/50

Rank 7:

iitjee08aspirant - 6/50

I know the marking scheme was tough. -7 for a wrong answer is probably a high number, but it is to promote sensible answering, and to minimize guesses. (Last year I lost lots of marks due to guesses)

The questions are tough (few of them), they have been taken from a leading physics professor's question paper. Hope you enjoyed it. I'll provide the solutions in a short while.

karthik2007

btw none of you got the 5th question right it seems.

feynmann

Hey , the 5th ans given by me is completely right !!!!!!!!

F = - dU/dx = dp/dt again p = h/

hence the ans .

Have u anything to say about it ?

karthik2007

Just hang on. I'll post the solutions.

karthik2007

Solutions:

1. Simple question. let i depend on t as i(t) = a+bt. Use boundary conditions and solve for i(t).

The required heat = _{[0 ]}

^{[10 ]} i(t)dt. - option a

2. Straightforward question, direct formula application.

3. differentiate partially wrt to y, and for maximum particle speed, put the cos term = 1 and equate it to 4fL.

4. Let the velocity of the bullet wrt ground be v'. Let the recoil velocity of the gun be some -u. Conserve momentum, and get the results. Answers are b and c.

5. Okay, this is a meaningless problem. In presence of a changing potential, the solution wont be a sine or a cosine wave, hence, potential is not defined. So let us consider the following approach.

If p be its momentum, and m its mass.

p²/2m + U(x) = constant

Put p = h/L

h²/2mL² + U(x) = constant

Diff both sides wrt to x, and get dL/dt = mL³/h² dU/dx

6. Frequency will be less than sqrt(k/m) . The total energy will contain a rotational term besides translational term. When we diff it wrt to to get the SHM equation, the effective m will be larger.

For the last 2 questions, I have typed the exact solutions given by the sir, for your benefit

@ feynmann - I directly compared your ans with the final ans as I dont have pen/paper with me atm. In case you get the ans on simplifying, do tell me.

feynmann

wrong !!

plz explain the following lines

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

h²/2mL² + U(x) = constant

Diff both sides wrt to x, and get dL/dt = mL³/h² dU/dx

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

How one could have got dL/dt by differentiating wrt 'x' ?

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