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 40cm3 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
1Q2) 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
1Just identify the systems and give the equations. I am utterly confused with them[17]
241)shouldnt it be c ???
assume vol of water=V cm3
initialy for balanacing system...
(V)(1)g=R -----(1)
and ball is balanced by its tension T .... T=W ---(2)
Finally ball is inside
Ball : 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'
1Yes eureka, i agree with your solution. But what about Q2) ?
1@d'artaganan for the second one it should be A)
by adding the bob we have added a mass of 10gm to the balance.
49actually no
coz the upthrust is balanced by an equal downthrust on the system
the upthrust forms an internal force for the stone water system
1OOOOOOOOOOOOO.....MR. ATGS KNOWS IT....
BUT I DIDNT GET WATEVER THING HE ****ED SO PLEASE EXPLAIN..
1Yeah..but........can you further clarify the difference between Q1) and Q2). What are the systems you are working on?
1the 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.
1Yes anirudh, you're correct. Thanx a lot, all of you...
I must slap myself :(