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 – F_{B}

$ \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