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Fluid Mechanics

Drag on a Sphere

A small spher...

Question

A small spherical ball (ping-pong ball) of weight 250 milli Newton and diameter 40 mm is subjected to a constant vertical velocity of 25 m/s of air density $1.2 k g / m^{3}$ . What is the drag coefficient?

A

0.42

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B

0.85

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C

1.0

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D

0.53

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Solution

The correct option is D 0.53
$F_{D} = C_{D} . \frac{ρ . A . V^{2}}{2}$
$250 \times 10^{- 3} = C_{D} . \frac{(1.2) \frac{π}{4} (0.04)^{2} \times 25^{2}}{2}$
$C_{D} = 0.53$

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