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Please help with DECELERATION problem!

  1. Jan 31, 2006 #1
    With motion problems, what formula do i use for deceleration of a particle if I am given v and a, and need to find distance?
     
  2. jcsd
  3. Jan 31, 2006 #2

    Päällikkö

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    For constant acceleration:
    x = x0 + v0t + (1/2)at2
     
  4. Jan 31, 2006 #3
    So, to find braking distance for each train in this problem:

    Two trains, one traveling at 72 km/h and the other at 133 km/h, are headed toward one another along a straight, level track. When they are 860 m apart, each engineer sees the other's train and applies the brakes. The brakes decelerate each train at the rate of 1.0 m/s2.

    would I use negative acceleration?
     
  5. Jan 31, 2006 #4
    and what do i do about the fact that time isn't specified in the question?
     
  6. Jan 31, 2006 #5
  7. Jan 31, 2006 #6
    vf^2=vi^2+2ad

    you are awesome
     
  8. Jan 31, 2006 #7
    I have another question: How do I go about this one:

    A drowsy cat spots a flowerpot that sails first up and then down past an open window. The pot was in view for a total of 0.35 s, and the top-to-bottom height of the window is 2.10 m. How high above the window top did the flowerpot go?

    I tried v=-gT+Vo and y=-.5gT^2+VoT
    but I think i'm missing something in the way the question is phrased.
    It gives total time, but no other numbers to plug in...
     
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