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: Acceleration equations involving time.

  1. Aug 24, 2011 #1
    At highway speeds, a certain car is capable of an an acceleration of about 1.7 m/s^2. At this rate, how long does it take to accelerate from 90 km/hr to 110 km/hr? (WATCH UNITS.)

    Given- Time=?

    Vf=vi+at Solve for t! T= vf-vi/a 110km/hr-90km/hr = 20km/hr

    How do I divide 20km/hr by 1.7 m/s^2?
  2. jcsd
  3. Aug 24, 2011 #2
    First convert your units to be in terms of meters and seconds then do the calculation.
  4. Aug 24, 2011 #3
    I got .02m but i'm not sure how to convert the hr to seconds
  5. Aug 24, 2011 #4
    What is that .02m?
    You want to convert km/hr to m/s.An hour has 60 mins and a min has 60 sec.
    [itex]\frac{1km}{hr}\frac{1hr}{3600s}\frac{1000m}{1km}= \frac {1000m}{3600s}[/itex]
  6. Aug 24, 2011 #5
    What I did now was 20(1000)/3600
    is 6m/s using sig figs and thats the answer! right?
  7. Aug 24, 2011 #6
    Yes if your teacher requires you to round up after every step.I would round after the final answer for time though.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook