23"Finally
Wboat+Wman=Upthrust"
is this the eqn after man has sunk ???
if yes then the upthrust = Wboat=Ïwater.Vnew, displaced by boat .g............. (1)
and since the man has sunk , the upthrust isnt able to balance its weight
hence Wman > Ïwater.Vnew, displaced by man .g .......(2)
add 1 and 2
Wman+Wboat > Ïwater.(Vnew, displaced by boat + Vnew, displaced by man .)g
Wman+Wboat > Ïwater.(Vnew, displaced by boat+man) g.........(3)
since from initial condition
Wman+Wboat = Ïwater.(Vold, displaced by boat+man) g................(4)
from 3 , 4
Vold, displaced by boat+man > Vnew, displaced by boat+man
hence level decreases
1Water level will decrease .
49suppose a block of ice in which a piece of iron is kept floats in water....what happens to water level after ice melts???????
49
Subhomoy Bakshi
·2009-12-18 08:42:28
yes if the cavity is not enclosed by ice....even if it is enclosed by ice, there is no diff if air is considered massless
`
1If an ice block with a cavity is floating and it melts, will the water level remain the same?
1
Unicorn--- Extinct!!
·2009-12-16 09:00:13
In case of cork..water level will remain same.
1
Unicorn--- Extinct!!
·2009-12-16 08:59:22
Iron ho ya aadmi, makes no difference.
1
Unicorn--- Extinct!!
·2009-12-16 08:56:37
http://targetiit.com/iit-jee-forum/posts/conceptual-11572.html
1357Now you all can solve this question
http://targetiit.com/iit-jee-forum/posts/dbt-13155.html
49
Subhomoy Bakshi
·2009-12-16 03:12:58
rite...........never read it........bt no one's trying #25
24ok....so man inside water means he is drowned ....i misunderstood it for floating....thx all.....
23
qwerty
·2009-12-16 00:56:43
subhomoy i gav the same explanation [3][3][3]
49
Subhomoy Bakshi
·2009-12-16 00:02:09
1))in a boat there is a tonne of cork kept.......
what happens to water level when
a) half of cork is thrown into water
b) all cork load is thrown into water
i)remain same, remain same
ii) decreases, still decreases
iii)decreases then increases
iv)increases still increases
v)increases n then decreases
2))what happens if the cork load was not there instead iron was kept
3))what happens if instead of cork ice was there??what would have happened after all ice melted???
49
Subhomoy Bakshi
·2009-12-15 23:56:02
yeah level decreases surely.....want a simple reason????
when man was in boat total wt of man n boat was balanced by upthrust U1
U1=Mg+mg
when man has sunk,
his wt is partly balanced by upthrust and partly by normal reaction at base.....
let total upthrust in this case be U2
so, U2+N=Mg+mg
so, U1>U2
so vol displaced at first > vol displaced later
so water level decreases
24
eureka123
·2009-12-15 21:32:38
Opinion changing now....[7][12]
initially
Wboat+man=Upthrust
=> Wboat+man=Ïwater.Vdisplaced.g
Here boat diplaces the liquid
Finally
Wboat+Wman=Upthrust
=> Wboat+Wman=Ïwater.Vdisplaced new.g
Here since bopat also floats..so volume diplaced remains same...but now extra volume is dislaced by man who is insdie water too....
so shouldnt level increase then ??
23
qwerty
·2009-12-15 10:58:15
@ light in the explanation that u gav wid dat fig ....i dont agree slightly
Is the volume of water displaced by man same when he is on the boat and after he has sunk ????
by the way just breaking head over it by only thinking isnt gona help , writing equations will make the concept clear cut
23
qwerty
·2009-12-15 10:52:46
level decreases ...
i apply a bit different logic wich i find it to be easy
substitute the man by water every where :
when the man is on the boat , put water in place of man such that mass of water = mass of man
so when u replace man by water , level doesnt change , so question remains unchanged since mg remains unchanged and hence the bouyant force
now after man has sunk , replace the man with the water such that mass of water that replaces man = mass of man
now since density of man is ofcourse gr8er than that of water ,
so u will require larger volume of water than that occupied by man
So when u will replace the man by the water , level will increase
This clearly shows that man after sinking had decreased the water level
1arey yaar, zyada dimag mat kharab karo..............water level will decrease
MAN JAO
1
biswajit
·2009-12-15 10:39:10
when the man was on the boat, the vol. displaced due to man is V
Ï=water density.......σ=man density
mg=VÏg
V0σ=VÏ
Vo=VÏ/σ
now σ>Ï
so Vo < V
hence,water level decrease
Ab samjhe biru???
1oh so i was too stupid.....[2]
1
biswajit
·2009-12-15 10:34:44
extra volume V has to be filled by water..........so level decrease
LIGHT..............is chees ko zyada light mat lo............ye hai bade kaam ki chees
24
eureka123
·2009-12-15 10:33:17
i also agree with light's explaination..becoz i too am thinking on same lines..
1I don't think in any way it'll decrease . and Light's explanation is correct.
1
biswajit
·2009-12-15 10:29:35
eureka,,,did u got my explaination??
1
biswajit
·2009-12-15 10:28:42
no..............it will certainly decrease
since the density of man is more than water
so he will occupy less volume of water and henceforth the extra volume of water has to be fulfiled by water and thereby decreasing the volume.
I hope it is correct
24
eureka123
·2009-12-15 10:28:03
ans given is decrease,,,,,
but i am sure level remains same....
any more replys ??
