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

Ok, a simple question

  1. Mar 21, 2004 #1
    car A & car B do 0-60mph in 4.3secs & 4.8secs respectively.
    both do 0-100mph in 11.6secs

    ?in a straight line race from standstill which car would be in front & by how much when they hit 100mph?
  2. jcsd
  3. Mar 22, 2004 #2
    Are we to assume that the acceleration from 0 to 60 mph is constant, and that the acceleration from 60 mph to 100 mph is constant (but different)?

    Anyway, you can solve this problem with one formula:
    [tex]V_f^2 = V_0^2 + 2ax[/tex]
    [tex]a = \frac{V_f - V_0}{t}[/tex]
    [tex]x = \frac{V_f^2 - V_0^2}{2\frac{V_f - V_0}{t}} = \frac{t}{2}(V_f + V_0)[/tex]

    Part 1: When the cars hit 60mph, car A will be at 57.6 meters and car B will be at 64.4 meters.
    Part 2: Car A's acceleration from 60 to 100 takes 7.3 seconds, whereas car B's takes only 6.8 seconds. The distance car A will pass between 60mph and 100mph is 261 meters, whereas car B will only pass 243.2 meters.

    The total distance of car A is 318.6 meters, and the total distance of car B is 307.6. So car A will be in front of car B by 11 meters when they both hit 100 mph.

    Of course, I'm not sure I'm right and I'm probably not. :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook