IIT JEE , AIEEE Forum - Physics , Mechanics

kavindra

arey yaar, tum sab kya kartey ho.

the formula for temp. variation of density is

p= p₀/(1+

T) [

is coeff. of cubical expansion]
the relation given by nishant is applicable only for slight temp. variations but this one is applicable for all. the nishant one can be derived by binomial expansion of the one above.

but why do we need it??? it is simple, obviously due to contraction on cooling, the same volume would weigh more in winter.{except for the anamolous behaviour of water}.
plz rate if satisfied.

tarinbansal

kavindra,
the weight will remain same.
See, mass depends on matter. When we are not changing the amount of matter taken, means that mass=constt.
mass= density x volume=constt
weight=density x volume x g=constt
so the weight will remain constant.

kavindra

arey, when density itself is changing acc. to the provided equation, so mass i.e. density X volume increases as density increases but volume remains constant i.e. 5 litres.

tarinbansal

YAAR,
How can mass change?
look,
mass=mass of one molecule x total no of molecules
now when the no of molecules are same, how can the mass change?
MASS DOESNOT DEPEND ON DENSITY VOLUME ETC.
IT DEPENDS ONLY ON THE MATTER CONTAINED WHICH IS NOT CHANGING IN THIS QUES.

kavindra

correct... I understand what u are saying.... but try to understand what i am saying.... they are talking about volume, not mass. Volume changes with temperature. This is the reason molality is preferred over molarity. as due to temp. change, the volume changes, so does concentration. Here the case is same. They took 5 litres at 300 K and another 5 litres at 270 K. Obviously, the 5 litres at 270 K are denser, so have more no. of molecules per unit volume, i.e. the same volume'll have more matter and hence more mass and obviously more weight. Am i clear???

kavindra

Oh now i understand how u are thinking... The sample'll obviously change. Lets look at it like this. Look they took 5 litres at 300 K, cooled it to lets say 270 K, so due to contraction, the volume decreased... So they had to add more kerosene to make it 5 litres again. Do you see the point??? They added more kerosene, bhai....

sagar90

DENSITY*VOLUME=MASS(WEIGHT)
IN SUMMER KEROSENE WILL EXPAND AND VOLUME WILL INCREASE AND DENSITY WILL DECREASE SO THAT WEIGHT IS SAME
WHILE IN WINTER KEROSENE WILL CONTRACT AND ITS VOLUME WILL DECRESE AND DENSITY WILL INCREASE KEEPING WEIIGHT CONSTANT

stavan110

Variatio in density with temperature is as follows:-

mass m = constant

m= V*density at initial temperature

m= V(1+

T) * new tempreture

now equate them and get answer

new density = initial density/1+

T

using binomial expansion we get answer that

initial density(1-

T) = new density

bhartibhanushali

see sagar u may be wrong

density *volume =mass
since volume is constant
mass depends upon density
density is inversely proportional to temp
hence if temp inc density dec
hence in summer {temp is high}
so mass is less
in winter {temp is low}
so mass is greater

hence for a constant volume of 5 ltr of kerosene
mass is greater during winter n smaller during summer

bhuwanaroracorroded

density decreases wid temperature

=

₀/[1+

T]

x4

OH MY GOD IT DEPENDS ON NATURE OF UR SYSTEM IF IT IS AN OPEN SYSTEM THEN KEROSENE WEIGHS LIGHTER IN SUMMER

BUT IF IT IS A CLOSED SYSTEM MASS REMAINS CONSTANT DESPITE SUMMER OR WINTER

x4

LOOK MASS IS AN INERTIAL FACTOR HOW DO U POEPLE BRING IN DENSITY ITS LIKE IF I FRY U ON A PAN WILL UR WT. INCREASE / DECREASE N
IF SYSTEM IS OPEN KEROSENE ESCAPES AS VAPORS N RATE OF VAPORISATION IS MAX DURING SUMMER .
CORRECT ME IF I AM WRONG THANK YOU

sagar90

bharti i think u didnt read d question carefully
see it is not given that volume is constant u may say 5 lit is given
but he had not given d volume in summer or winter
and even if he had given that then also i think d mass would not change
and of course i m talking about a closed system

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