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Question Number 66621 by lalitchand last updated on 17/Aug/19

Commented by lalitchand last updated on 17/Aug/19

$8 iii$
Commented by mr W last updated on 18/Aug/19

$a n s w e r g i v e n i n b o o k f o r Q 8 (i i) i s w r o n g .$ $Q 8 (i i i) i n b o o k i s n o t c l e a r . i f w e i g h t$ $o f 1 k g (s t o n e) i s 10 N i n w a t e r, t h e n$ $t h e d e n s i t y o f w a t e r m u s t b e z e r o,$ $n o m a t t e r w h a t d e n s i t y t h e s t o n e h a s .$ $t h e a n s w e r i n b o o k i s 10 g / c c, b u t n o$ $s t o n e i n t h i s w o r l d c a n h a v e s u c h a$ $l a r g e d e n s i t y .$ $\Rightarrow b o o k i s b a d$
Commented by mr W last updated on 18/Aug/19

$q u e s t i o n i s w r o n g, a n s w e r i s w r o n g .$ $a n s w e r t o q u e s t i o n 8 (i i) i s a l s o w r o n g .$
Commented by lalitchand last updated on 18/Aug/19

$some one says answer is 4 g / {cm}^{3}$
Commented by lalitchand last updated on 18/Aug/19

$That means question is wrong$
Commented by mr W last updated on 18/Aug/19

$a c o r r e c t q u e s t i o n 8 (i i i) c o u l d b e :$ $i f t h e w e i g h t o f 2 k g s t o n e i s 10 N i n$ $w a t e r, w h a t i s t h e d e n s i t y o f t h e s t o n e ?$ $t h e a n s w e r w e r e 2 g / {c m}^{3} .$ $s o l u t i o n :$ $l e t V = v o l u m e o f s t o n e, d e n s i t y i s ρ,$ $m a s s i s m .$ $V = \frac{m}{ρ}$ $u p t r u s t g i v e n b y w a t e r i s ρ_{W} g V$ $w e i g h t o f s t o n e i n w a t e r i s t h e n$ $G_{W} = m g - ρ_{W} g V = m g (1 - \frac{ρ_{W}}{ρ})$ $w i t h m = 2 k g, G_{W} = 10 N, ρ_{W} = 1 g / {c m}^{3}$ $2 \times 10 (1 - \frac{1}{ρ}) = 10$ $\Rightarrow 1 - \frac{1}{ρ} = \frac{1}{2}$ $\Rightarrow ρ = 2 g / {c m}^{3}$
Commented by mr W last updated on 18/Aug/19

$y o u c a n a l s o s e e t h a t i t i s i m p o s s i b l e$ $t h a t 1 k g s t o n e h a s a w e i g h t o f 10 N$ $i n w a t e r, b e c a u s e t h a t w o u l d r e q u e s t$ $1 \times 10 (1 - \frac{1}{ρ}) = 10$ $b u t t h i s i s n o t p o s s i b l e . t h e r e f o r e$ $t h e q u e s t i o n i n t h e b o o k i s w r o n g .$
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