Unit 38: Terminal Velocity, Sedimentation, & Centrifugation
Practice Problems
Note: problem difficulty is ranked using a star system.
(*) One-star problems are fundamental to the unit, and can be done relatively quickly. Use these problems to introduce yourself to the material.
(**) Two-star problems are more difficult, and require an understanding of one or two key concepts. Use these problems to test your understanding of the material.
(***) Three-star problems are the most difficult, and require some creative thinking in addition to a deep familiarity with multiple key concepts. Use these problems to challenge yourself; if you can complete one of these, you’re on your way to mastering the material.
*Q38.1) Calculate the terminal velocity of a grain of sand of radius 1mm and density 2000 kg/m³ as it sediments through water.
***Q38.3) A protein molecule of density 1200 kg/m³ and molar mass 5 x 10⁶ g/mol is placed in a water-filled ultracentrifuge tube at a distance of 5cm from the rotation axis and spun at 40 000 rpm.
a) What’s the terminal velocity of the protein?
b) How long will it take the protein to sediment 1 cm?
**Q38.2) A 100g ice cube of density 950 kg/m³ is submerged in water and released, causing it to move towards the surface at a terminal velocity of 20cm/s. What’s the friction factor between the water and the ice cube?