Question 350221
<font face="Garamond" size="+2">


Your answer for speed is correct. In the first 20 minutes, going 60 miles per hour which is the same thing as 1 mile per minute, the car travels 20 miles.  In the next 30 minutes, going 30 miles per hour, which is *[tex \Large \frac{1}{2}] mile per minute, the car travels 15 miles.  Total distance:  20 plus 15 is 35 miles.  Total time 50 minutes which is *[tex \Large \frac{5}{6}] hour, so:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ r\ =\ \frac{d}{t}\ =\ \frac{35}{\frac{5}{6}}\ =\ 35\,\cdot\,\frac{6}{5}\ =\ 42\text{ mph}] average SPEED.


Notice that speed, being a scalar quantity, doesn't take into consideration the direction of travel.


Velocity, on the other hand, is a vector quantity.  It has a magnitude (the scalar speed) and a direction.  So if the car went 20 miles east and then turned around and traveled 15 miles west, the car would be 5 miles east of the starting point.  5 miles in *[tex \Large \frac{5}{6}] of an hour.


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ r\ =\ \frac{d}{t}\ =\ \frac{5}{\frac{5}{6}}\ =\ 5\,\cdot\,\frac{6}{5}\ =\ 6\text{ mph}]


and since the ending point was due east of the starting point, the velocity is 6 mph EAST.


John
*[tex \LARGE e^{i\pi} + 1 = 0]
My calculator said it, I believe it, that settles it
<div style="text-align:center"><a href="http://outcampaign.org/" target="_blank"><img src="http://cdn.cloudfiles.mosso.com/c116811/scarlet_A.png" border="0" alt="The Out Campaign: Scarlet Letter of Atheism" width="143" height="122" /></a></div>
</font>