2. (a) Sand dunes in a desert move over time as sand is swept
up the windward side to settle in the lee side. Such “walking”
dunes have been known to walk 20 feet in a year and
can travel as much as 100 feet per year in particularly
windy times. Calculate the average speed in each case in
m/s. (b) Fingernails grow at the rate of drifting continents,
on the order of 10 mm/yr. Approximately how long
did it take for North America to separate from Europe, a
distance of about 3 000 mi?