A metal cube of edge 5 cm and density 9.0 g cm^-3 is suspended by a thread so as to be completely immersed in a liquid of density 1.2 g cm^-3. Find the tension in thread. (Take g = 10 m s-2)
[Hint: Tension in thread = apparent weight of the cube in liquid]

Edges of cube = 5 cm

∴ Volume = 5 × 5 × 5 = 125 cm³

Density of metal = 9.0 g cm^-3

Density of liquid = 1.2 g cm^-3

Mass of the cube = volume of the cube × density of the cube

= 125 × 9

= 1125 g

Upthrust on cube = volume of the cube × density of the liquid × g

= 125 × 1.2 × g

= 150 gf

Tension in thread = Apparent weight of the cube in liquid

= true weight – upthrust

= 1125 – 150

= 975 kgf

= 9.75 N    [∵ g = 10 ms^-2]

Hence, tension in thread = 9.75 N