Posted by Peter Adrian Ngo on Sunday, March 20, 2011 at 3:38am.
A car going 50mi/h overtakes and passes another car moving at 45 mi/h. what length of road is required for the operation? assume that each car is 15 ft long and that there is a 60ft space between them before and after passing. taking into account the approach of a car from the opposite direction at 50 mi/h, what clear length of road is required?

Physics  drwls, Sunday, March 20, 2011 at 8:06am
One car passes the other at a relative rate of 5 mph = 7.333 ft/s, and must change the distance between them by 60 + 60 + 15 = 135 feet before returning to the right side of the dividing line. The time required for the entire passing maneuver is 135/7.333 = 18.41 s. An oncoming car approaches the passing car at a relative rate 100 mph = 146.7 ft/s. The clear length of road required to avoid a collision is
146.7 x 18.41 = 2700 feet, which is over half a mile. 
Physics  vdes, Tuesday, August 5, 2014 at 9:17am
12