Calculating Avg Velocity of Car in Rural Rally

[catherines]

Homework Statement

The motion depicted in Figure 1 shows the path of a team in a car rally held in a rural area where the speed limit is 80 km/h. In the car rally, points are deducted for anyone determined to be breaking the speed limit.

c) Determine the average velocity (magnitude and direction) of the car's motion for the entire trip.

The race track kind of looks like the one I attached.


side A = 23 km = side C
side B = 46 km
that small part, D = 15 km
x = start
v, >, <, ^ show the direction.

Homework Equations

Vavg = (delta x)/(delta t)

The Attempt at a Solution

(I already did the first parts)
The total displacement (delta x) is from x to D. So that would be 46-15 = 31 km.
Total time is ?? Assuming that they don't surpass the speed limit, they are going 80km/h. Knowing that, and that they go a total of 107 km... (46+23+23+15) ... they will take 1. 3375h. So...then wouldn't it be 31/1.3375 = 23.1 km/h [E] (East because displacement is only eastward)

The answer the book gave was 25 km/h [E].
What'd I do wrong??

 

[Doc Al]

Your answer looks OK to me. (Even though you assume that the car always travels at its maximum speed. )

 

[catherines]

Silly textbook...

Thanks!