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2 Physics Questions

  1. Oct 7, 2003 #1
    Hi,

    I'm having trouble with two physics problems.

    - Ashley runs 3.0 km in 4.00 minutes. What is her average velocity? The answer is 45 but I can't figure out how to get it.

    - A train moving at 15 km/hr takes 1 minute to come to a stop, find its rate of acceleration, its average velocity and the distance it takes to stop.

    Rate of Acceleration
    --------------------

    15/60 = .25

    Average Velocity
    ----------------

    Need help finding this

    Distance
    --------

    15/3.6 = 4.16

    4.16 m/s
    -------- = .069 m/s^2
    60s

    Thanks!
     
  2. jcsd
  3. Oct 7, 2003 #2
    - Ashley runs 3.0 km in 4.00 minutes. What is her average velocity? The answer is 45 but I can't figure out how to get it.

    Use the equation
    v=d/t
    v=3/4

    - A train moving at 15 km/hr takes 1 minute to come to a stop, find its rate of acceleration, its average velocity and the distance it takes to stop.

    To find your average velocity, use the same equation as I used above (do it yourself this time so you learn.)
     
  4. Oct 7, 2003 #3
    Thanks quantum!

    I got 3/4 = .75 = .75*60 = 45 for the first one...

    For the second one I got 15/60 = .25*60 = 15...

    Thanks again!
     
  5. Oct 8, 2003 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    metioguy04: Let me suggest you do something that quantum also did not do: Write the units with the answer!

    You asserted that the answer was 45.

    Well, no, the answer CAN'T be 45. The answer has to be a speed and 45 is a number, not a speed. That might seem picky but had you written 45 km/HOUR it would have been a heckuvalot easier to see what to do. Since you gave the time in minutes, the natural thing to do is to answer in km/min.
     
  6. Oct 9, 2003 #5
    LOL! Looked right over that... Sorry.
     
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