TargetIIT

Q1)

Figure shows a weigh bridge, with a beaker P with water on one pan and a balancing weight R on the other. A solid ball Q is hanging with a thread outside water. It has volume 40cm[p]3[/p] and weighs 80gms. If this ball is to be lowered to fully sink in water, but not touching the beaker any where, the balancing weight R' would be?

a) same as R   b) 40g less than R   c) 40g more than R   d) 80g more than R
[image]41191024.jpg[/image]

Q2) A beaker with a liquid of density 1.4 g/cc is in balance over one pan of a weighing machine. If a solid ball of mass 10 gm and density 8 gm/cc  is now hung from the top of the pan with a thread and sinking fully in the liquid without touching the bottom, the extra weight to be put on the other pan for balance will be :

a) 10gm  b) 8.25gm c) 11.75gm  d) -1.75g
[image]41191560.jpg[/image]

Just identify the systems and give the equations. I am utterly confused with them[17]

ans 1)  option D

1)shouldnt it be c ???
assume vol of water=V cm[p]3[/p]
initialy for balanacing system...

(V)(1)g=R   -----(1)

and  ball is balanced by its tension T   .... T=W  ---(2)

Finally ball is inside

[u]Ball[/u]  :   T' +U=W

on beaker this U is extra force...acts on base of beaker  where U=(40)(1)g

So
V(1)g +40(1)(g)=R'
=>  R+40g=R'

yeah bhaiya i made a mistake . for 1) your answer is correct.

Yes eureka, i agree with your solution. But what about Q2) ?

@d'artaganan for the second one it should be A)

by adding the bob we have added a mass of 10gm to the balance.

won't the upthrust affect the reading?

actually no

coz the upthrust is balanced by an equal downthrust on the system

the upthrust forms an internal force for the stone water system

OOOOOOOOOOOOO.....MR. ATGS KNOWS IT....

BUT I DIDNT GET WATEVER THING HE ****ED SO PLEASE EXPLAIN..

Yeah..but........can you further clarify the difference between Q1) and Q2). What are the systems you are working on?

the difference between the first and the second is the tension.
in first tension acts on external body thus we count only the upthrust.

but in second tension acts on the system being weighed thus whole weight of the immersed body is counted.

what we have to look at is the net force acting on the balance.

Yes anirudh, you're correct. Thanx a lot, all of you...



[hide]I [b]must[/b] slap myself :([/hide]