Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Race Rally

  1. Jun 15, 2008 #1
    1. The problem statement, all variables and given/known data

    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.

    2. Relevant equations

    Vavg = (delta x)/(delta t)

    3. 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??

    Attached Files:

    • 7.jpg
      File size:
      6.2 KB
  2. jcsd
  3. Jun 15, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your answer looks OK to me. (Even though you assume that the car always travels at its maximum speed. :wink:)
  4. Jun 15, 2008 #3
    Silly textbook...

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook