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Homework Help: One dimensional motion of car

  1. Jan 27, 2010 #1
    1. The problem statement, all variables and given/known data

    A car accelerates uniformly from rest to a speed of 40 mi/h in 12.0 secs find A) the distance the car traveled during this time and B) the constant accelaration of the car

    2. Relevant equations

    a) Displacement of an object as a function of time: delta x =1/2(v0+v)T
    B) Velocity as a function of discplacment = v^2= v0^2 + 2a delta x

    3. The attempt at a solution
    A) delta x = 1/2(0 + 20 m/s) 12
    answer for part a = delta x = distance =120 m is this right?

    B)(20 m/s)^2= 0^2 + 2a(120m)
    400 m^2/s^2= 240ma
    cross cancellation = answer for part b constant accelaration= 1.666666667= approx 2 m/s^2
    Is this right?
  2. jcsd
  3. Jan 27, 2010 #2
    Your equations are right, but your conversion from mph to m/s is not quite correct. It's not exactly half, it's more like 0.447
  4. Jan 27, 2010 #3
    I'm sorry, what do you mean.

    40 mi/h x 1h/60min x 1min/60 sec x 1609m/ 1 mi = 17.87777778 m/s but since there is only one sig fig i rounded it up to twnety. is that not how i should have gone about converting it?
  5. Jan 27, 2010 #4
    No, you did the conversion correctly, but you shouldn't worry about sig figs until the very end. Keep the 17.88 and then round when you're done. If your teacher told you otherwise, then your answer is right and you're done :)
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