Question 20N.3.HL.TZ0.12

incompressible ✓

non-viscous ✓

laminar/streamlined flow ✓

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.

$F=mg-\rho Vg$

OR

$F=\left(0.0126\times 9.81\right)-\left(915\times 7.24\times {10}^{-6}\times 9.81\right)$ ✓

$F=5.86\times {10}^{-2} «\mathrm{N}»$ ✓

Accept use of $g\mathit{=}\mathit{10}$ leading to $F=\mathit{6}\mathit{.}\mathit{0}\mathit{\times }{\mathit{10}}^{\mathit{-}\mathit{2}}\mathit{ }N$

$Q=«2\mathrm{\pi }\times \frac{\mathrm{energy} \mathrm{stored}}{\mathrm{energy} \mathrm{lost}}=2\mathrm{\pi }\times \frac{100}{10}=» 63$ ✓

drag force increases OR damping increases OR more energy lost per cycle ✓

$\mathrm{Q}$ will decrease ✓