Physics MCQs thread.

[intel1993]

can any one plz explain the answer??

 

[Saturation]

hey can anybody plz explain me the question 21 from j2002......................

Q)A mass of liquid of density (p) is thoroughly mixed with an equal mass of another liquid of density(2p). No change of the total volume occurs...
Waht is the density of the liquid mixture?

A) 4/3 p
B) 3/2 p
C) 5/3 p
D) 3 p

Liquid 1
mass = m
volume = v
density = p

liquid 2
mass = m
density = 2p
volume = 0.5v ( since the mass must be the same, to "balance" the 2p density, the volume must be half)

total density = m/v
which is:
2m/0.5v+v ,which works out to 4/3 (m/v)
so the answer is 4/3 (p)

 

[sakibfaiyaz]

the answer is C,
Shouldn't it be D?
What exactly do they mean by "a" given cross sectional area. I infer they mean it could be "any" cross section.
So if we find the no.electrons passing through UNIT cross section, it gives us D

 

[yubakkk]

use nq=it
n=10*30/1.6*10^-19

 

[sakibfaiyaz]

Sorry but that in no way answers my question. I arrived at 6.3*10^-21, but wouldnt there be further step(s) to get no.of electrons per UNIT area?

 

[hassam]

its shud be B cos i is also proportional with frequency square

 

[sakibfaiyaz]

Hassam could you answer my question?

 

[yubakkk]

Sorry but that in no way answers my question. I arrived at 6.3*10^-21, but wouldnt there be further step(s) to get no.of electrons per UNIT area?

i think is write then wat could be that step??

 

[yubakkk]

no one knows this ?? none of u are giving ans yar//////
any one try??

 

[RafaySid]

Well as far as I know of the only solution, using dsinθ=nλ, as d and λ are constants, we equate n/sinθ. So 3/sin45 = x/sin90, hence x=4.24.. ~ 4. anybody got a more simpler working?? Please answer.

 

[arlery]

how can I solve this one?

 

[WellWIshER]

i think da ans is b?

 

[ahmed t]

well here as half the water will travel to the othr container the hieght will drop to half, and also the mass, as there will only be half as much water in that side
so it will be B

 

[WellWIshER]

well here as half the water will travel to the othr container the hieght will drop to half, and also the mass, as there will only be half as much water in that side
so it will be B

yups!

 

[Xthegreat]

m/j 04 q9

 

[Xthegreat]

a molecule of mass m travelling horizontally with the velocity u hits a vertical wall at right angles to the wall. it then rebounds horizontally with the same speed. what it is the change in momentum?
a. zero
b. mu
c. -mu
d. -2mu

 

[arlery]

d - 2mu

 

[Xthegreat]

d - 2mu

why?

 

[Abdulrab]

guys the answer in the marking scheme is B !! i even dont know how to do it !!!

 

[arlery]

d - 2mu

why?

because it's traveling with a momentum mu, when it rebounds, it travels in the opposite direction hence it will be -mu

final momentum - initial momentum = -mu-mu = -2mu