5.2 Drag Forces

The terminal velocity of a person falling in air depends upon the weight and the area of the person facing the fluid. Find the terminal velocity (in meters per second and kilometers per hour) of an 80.0-kg skydiver falling in a headfirst position with a cross-section area facing the fluid of $0 . \text{140} \text{ m}^{2}$.

A 560-g squirrel with a cross-section area facing the fluid of $\text{144} \text{ cm}^{2}$ falls from a 5.0-m tree to the ground. Estimate its terminal velocity. (Use a drag coefficient for a horizontal skydiver.) What will be the velocity of a 56-kg person hitting the ground, assuming no drag contribution in such a short distance?

By what factor does the drag force on a car increase as it goes from 65 to 110 km/h?

Using Stokes’ law, verify that the units for viscosity are kilograms per meter per second.

Stokes’ law describes sedimentation of particles in liquids and can be used to measure viscosity. Particles in liquids achieve terminal velocity quickly. One can measure the time it takes for a particle to fall a certain distance and then use Stokes’ law to calculate the viscosity of the liquid. Suppose a steel ball bearing (density $7 . 8 \times \text{10}^{3} \text{ kg}/\text{m}^{3}$, diameter $3 .\text{0 mm}$) is dropped in a container of motor oil. It takes…