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Dont know where I am wrong.......
I solved this question by 2 diff methods and am getting answers diff.....plzz tel my mistake
Q A sphere of 5 kg specific gravity 2 is completely submerged into water.Find radius of sphere
method 1
Volome of sphere=mass /density =5/(2*103)=4/3 πr3
=>r=√(15*10-3/8π )
method2
Upthrust=Gravity
=>VÏwg=mg
=>(4/3 πr3)(103)=5
=>r=√(15*10-3/4π)
where is the mistake?????????[7][7][7]
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13 Answers
106upthrust=mg is valid only for floatation
ur first method seems correct.
4Ï€r3/3 = 5/2000
==> r3 = 15/8000Ï€
==> r = (3√15/Ï€)/20
24at floatation??????????[11][11]
when a body will float it wont displace any fluid so how will upthrust act?
i hope i am not seriously going wrong way today
106i meant to say at any position where it is in equilibrium only....................as it's specific gravity is 2, it will touch the bottom of the container so, there will be a normal force as well.
33yeah u are right...
it will sink..
so density=mass/volume.. will give radius..
1no it is not wrong eureka..
but it cant give u exact value...
infact u can check your answer 1 by this second method.....
only u shud replace = by <= to check but it cant give u exact answer...
note the factor 2... if specific gra.. wud have been 1 had the answer been correct in both cases????
9actually method 2 is only right
cos u dont no if its hollow or not
106well then u also need 2 know if its floating.... or some other condition needs to be given.
1@ ashish its given that specific gr =2
so it has to get submerged in water even if it is not given directly..
24yup philip is rite..............method 2 doesnt work here..............and as already stated there will be some normal reaction from bottom of surface......[1][1]