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Calculate the Reynolds number N′R for a ball with a 7.40-cm diameter thrown at 40.0 m/s.

Strategy

We can use the Reynolds number equation calculate N’_R , since all values in it are either given or can be found in tables of density and viscosity.

Solution

We first find the kinematic viscosity values:

Substituting values into the equation for N’R yields:

Discussion

This value is sufficiently high to imply a turbulent wake. Most large objects, such as airplanes and sailboats, create significant turbulence as they move. As noted before, the Bernoulli principle gives only qualitatively-correct results in such situations.

Reference : OpenStax College,College Physics. OpenStax College. 21 June 2012.
http://openstaxcollege.org/textbooks/college-physics
Creative Commons License : http://creativecommons.org/licenses/by/3.0/

Find the terminal velocity of an 85-kg skydiver falling in a spread-eagle position.

where Vt is the terminal velocity, m is the mass of the skydiver, g is the acceleration due to gravity, C_d is the drag coefficient, ρ is the density of the fluid through which the object is falling, and A is the projected area of the object.

Reference : OpenStax College,College Physics. OpenStax College. 21 June 2012.
http://openstaxcollege.org/textbooks/college-physics
Creative Commons License : http://creativecommons.org/licenses/by/3.0/

where h is skydiver height and w the width at “spread-eagle” position