HOW DO YOU DO THIS QUESTION ?

Question

A student wanted to drive from Austin to

San Antonio, 80 miles south of Austin on

highway I35. Unfortunately, he entered the

highway in the wrong direction and drove all

the way toWaco — 100 miles north of Austin

— before he noticed his error. In Waco,

he turned around, drove back to Austin and

continued to San Antonio. The whole trip

took 5.17 hours.

What was the student’s average speed dur-

ing this trip? Answer in units of MPH.

Answer 1

This question involves the subtle, but important difference between speed and velocity.

The car traveled a total of 280 mile in spite of the fact that it finished only 80 miles from where it started.

The car traveled the 280 at an average SPEED of 54.159 mph. (280/5.17=54.159)

However, the average VELOCITY was only 15.474 mph.

(80/5.17=15.474)