1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help needed with accelleration problem !

  1. Jan 20, 2005 #1
    help needed with accelleration problem...urgent!

    I am having trouble wiht one of the questions on my first physics HW asignment.
    I've tried solving it different ways but cant seem to get the correct answer.

    the question reads:
    An engineer in a locomotive sees a car stuck on the track at a railroad crossing in front of the train. When the engineer first sees the car, the locomotive is 280m from the crossing, and its speed is 24m/s.
    if the engineer's reaction time is .55s, what should be the magnitude of the minimum deceleration to avoid an accident?

    I have been using the formula:
    Vfinal^2 - Vinitial^2 = 2a(xfinal - xinitial)

    V being velocity, a being accelleration and x being position.

    I solve this equation for a and begin substituding in.
    I know that my Vinitial is 280 - 34(.55) because you have to take out ground covered in the engineers reaction time.

    but when I substitute in everything else I alwasy get -1.079
    because of the wording of the question I have tried it with and without the negative sign, but it is still wrong.

    any help would be greatly appreciated
    pedro
     
  2. jcsd
  3. Jan 20, 2005 #2

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    The sign should be minus,because it's a DECELERATION.The modulus is much,much smaller than what u've gotten.Since the logics and the formula u used are good (24*0.55,not 34*0.55,okay??),i advide you to check the arithmetics...

    Daniel.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Help needed with accelleration problem !
Loading...