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9-1.Fluid Mechanics
normal
Eight spherical rain drops of the same mass and radius are falling down with a terminal speed of $6\, cm -s^{-1}$ . If they coalesce to form one big drop, what will be the terminal speed of the bigger drop ? (Neglect the buoyancy of the air) ....... $cm -s^{-1}$
A$1.5$
B$6$
C$24$
D$32$
Solution
$\mathrm{R}=\mathrm{n}^{1 / 3} \mathrm{r}=8^{1 / 3} \mathrm{r}=2 \mathrm{r}$
$\frac{V_{T_{1}}}{V_{T_{2}}}=\left(\frac{R_{1}}{R_{2}}\right)^{2}$
$\mathrm{V}_{\mathrm{T}_{2}}=6 \times 4$
$\mathrm{V}_{\mathrm{T}_{2}}=24 \mathrm{cm} / \mathrm{s}$
$\frac{V_{T_{1}}}{V_{T_{2}}}=\left(\frac{R_{1}}{R_{2}}\right)^{2}$
$\mathrm{V}_{\mathrm{T}_{2}}=6 \times 4$
$\mathrm{V}_{\mathrm{T}_{2}}=24 \mathrm{cm} / \mathrm{s}$
Standard 11
Physics
