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Question 20N.3.HL.TZ0.12b

Date	November 2020	Marks available	[Maximum mark: 3]	Reference code	20N.3.HL.TZ0.12b
Level	HL	Paper	3	Time zone	TZ0
Command term	Determine	Question number	b	Adapted from	N/A

b.

[Maximum mark: 3]

20N.3.HL.TZ0.12b

A sphere is dropped into a container of oil.
The following data are available.

Density of oil $= 915 kg m^{- 3}$
Viscosity of oil $= 37.9 \times 10^{- 3} Pas$
Volume of sphere $= 7.24 \times 10^{- 6} m^{3}$
Mass of sphere $= 12.6 g$

(b)

Determine the terminal velocity of the sphere.

[3]

Markscheme

radius of sphere $= 0.012 « m »$ ✓

weight of sphere $= 6 π η r v + ρ V g$

OR

$v = \frac{(1.26 \times 10^{- 2} - 915 \times 7.24 \times 10^{- 6}) \times 9.81}{6 π \times 37.9 \times 10^{- 3} \times 1.2 \times 10^{- 2}}$ ✓

$v = 6.84 « m s^{- 1} »$ ✓

Accept use of $g = 10$ leading to $v = 7.0 « m s^{- 1} »$

Allow implicit calculation of radius for MP1

Do not allow ECF for MP3 if buoyant force omitted.

Examiners report

Only those candidates who forgot to include the buoyant force missed marks here.

Syllabus sections

Option B: Engineering physics

Option B: Engineering physics » Option B: Engineering physics (Additional higher level option topics) » B.3 – Fluids and fluid dynamics (HL only)

Option B: Engineering physics » Option B: Engineering physics (Additional higher level option topics)