help needed with accelleration problem...urgent!

[pedro]

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

[dextercioby]

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.