Q.
If the terminal speed of a sphere of gold (density =19.5kg/m3) is 0.2m/s in a viscous liquid (density =1.5kg/m3), find the terminal speed of a sphere of silver (density =10.5kg/m3) of the same size in the same liquid.
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AIEEEAIEEE 2006Mechanical Properties of Fluids
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Solution:
Terminal speed of spherical body in a viscous liquid is given by vr=9η2r2(ρ−σ)g
where ρ= density of substance of body σ=density of liquid
From given data vT(Gold)vT(Ag)=ρGold−σlρAg−σl ⇒vT(Ag)=19.5−1.510.5−1.5×0.2=189×0.2 =0.1m/s