IB Physics HL A.2.10 Viscous drag and terminal-speed models Question Bank

Practise IB Physics HL A.2.10 by analysing viscous drag, force balance and quantitative terminal-speed models.

Exam points

Derive or use a terminal-speed relation from drag, weight and buoyancy forces.
Analyse how radius, density or fluid properties alter terminal speed.
Evaluate a drag model using assumptions about Reynolds number, shape and fluid behaviour.

[Maximum number: 4]

A solid sphere is released from rest below the surface of a fluid and begins to fall.

(a)

Explain why the sphere will reach a terminal speed.

[ 2 ]

(b)

The weight of the sphere is 6.16 mN and the radius is $5.00 \times 10^{-3} \mathrm{~m}$ . For a fluid of density $8.50 \times 10^{2} \mathrm{~kg} \mathrm{~m}^{-3}$ , the terminal speed is found to be $0.280 \mathrm{~ms}^{-1}$ . Calculate the viscosity of the fluid.

[ 2 ]

any evidence (numerical or algebraic) of a realisation that
$\begin{aligned} 6 \pi \eta r+\rho g V=W \vee \| \eta=\frac{6.16 \times 10^{-3}-4.366 \times 10^{-3}}{6 \pi \times 0.005 \times 0.280} \text { » } \eta=0.0680 \text { «Pas» } \end{aligned}$

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A.2.10—Viscous drag question 1

Question (a)

Question (b)