fisica1-youn-e-freedman-exercicios-resolvidos

2.53: a) The change in speed is the area under the a x versus t curve between
vertical lines at t = 2.5s
and t = 7.5s.
This area is
2
2
1 (4.00 cm s + 8.00cm s )(7.5 s − 2.
5 s) = 30.0 cm s
2
This acceleration is positive so the change in velocity is positive.
b) Slope of v x versus t is positive and increasing with t.
2.54: a) To average 4 mi hr , the total time for the twenty-mile ride must be five
hours, so the second ten miles must be covered in 3.75 hours, for an average of 2.7
mi hr. b) To average 12 mi hr , the second ten miles must be covered in 25 minutes and
the average speed must be 24 mi hr.
c) After the first hour, only ten of the twenty miles
have been covered, and 16 mi hr is not possible as the average speed.