Question 20N.2.SL.TZ0.12b

radius of sphere$=0.012 «\mathrm{m}»$ ✓

weight of sphere$=6\pi \eta rv+\rho Vg$

OR

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

$v=6.84 «\mathrm{m} {\mathrm{s}}^{–1}»$ ✓

Accept use of $g\mathit{=}\mathit{10}$ leading to $v\mathit{=}\mathit{7}\mathit{.}\mathit{0}\mathit{ }«\mathrm{m} {\mathrm{s}}^{–1}»$

Allow implicit calculation of radius for MP1

Do not allow ECF for MP3 if buoyant force omitted.