Teaching Physics with the Physics Suite
Edward F. Redish
Making up a lap
Jeff Gordon and Dale Earnhardt are racing their stockcars to try to win the Daytona 500. Jeff makes a pit stop to gas up and change his tires. When he gets back on the track, he discovers that he is right next to Dale. Both are traveling at speeds of 150 mi/hr, but Dale is one full lap (2.5 miles) ahead.* Jeff wants to catch Dale so he decides to try to accelerate slowly and uniformly (constant a) until he catches Dale – so that after Dale has done 10 laps, Jeff will have done 11. (Jeff knows from studying physics that uniform acceleration will use less gas.)
* For those not familiar with NASCAR racing, in this race the cars travel around a 2.5 mi oval track 200 times. During the long time that this race takes, cars have to make pit stops for service – gas, new tires, etc.
(a) How much time does he have to do it, assuming that Dale keeps a constant speed during those 10 laps?
(b) What distance will Jeff have to cover in that time?
(c) Again, assuming that Dale keeps a constant speed, what does Jeff’s average speed have to be in order to catch Dale after Dale has gone 10 laps?
(d) What was Jeff’s acceleration during the time Dale was going 10 laps?
(e) What would Jeff’s speed be when he catches Dale?
Page last modified Spetember 20, 2009: K25