Q: A brass sphere weighs 100 gm.wt in air. It is suspended by a thread in a liquid of specific gravity = 0.8. If the specific gravity of brass is 8, the tension in the thread in newtons is.
(a) 0.0882
(b) 8.82
(c) 0.882
(d) 0.00882
Ans: (c)
Sol: Tension = Weight – Buoyancy
T = Mg – FB
$ \displaystyle T = Mg (1 – \frac{d_l}{d_s})$
$ \displaystyle T = Mg (1 – \frac{0.8 d_w}{8 d_w})$
$ \displaystyle T = Mg (1 – \frac{1}{10})$
$ \displaystyle T = Mg ( \frac{9}{10})$
$ \displaystyle T = 0.9 \times Mg $
$ \displaystyle T = 0.9 \times 100 \times 10^{-3}\times 9.8 $
T = 0.882 N