A 0.5 kg block of brass (density; 8 x ${10}^3 \mathrm{kg} {\mathrm{m}}^{-3})$ is suspended from a string. What is the tension in the string if the block is completely immersed in water?
(g = l0 ${\mathrm{ms}}^{-2}$)?

Volume of block = $\frac{0.5}{8\times {10}^3}{\mathrm{m}}^3$

Volume of displaced water = $\frac{0.5}{8\times {10}^3}{\mathrm{m}}^3$

Weight of displaced water = $\frac{0.5}{8\times {10}^3}{10}^3\times 10 \mathrm{N}$

                                           = $\frac{5}{8}\mathrm{N}$

 This is equal to upward buoyant force.

Tension in string in actual weight less the upward buoyant force. So, tension is $[5-\frac{5}{8}]\mathrm{N}.$