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Homework Help: Calculate the time at which the object changes direction

  1. Aug 3, 2017 #1
    1. The problem statement, all variables and given/known data
    An object starts from rest and uniformly acquires a velocity of 20.0 m/s in 5.0 minutes. For the next 10. minutes the object moves with a constant speed. After 10. minutes moving at 20. m/s the object then again accelerates and reaches a speed of 15 m/s in the opposite direction in 3.0 minutes time.

    Calculate the time at which the object changes direction

    2. Relevant equations

    3. The attempt at a solution
    made velocity time graph. tried to find the equation y=mx + b. already knew that slope + -.19 unknown what b is and i found that velocity = 0 when time is at 1005.275 seconds however it said this was wrong. I am very confused and jumbled. Unsure how to find displacement since it crosses the x axis and moves into negative.
  2. jcsd
  3. Aug 3, 2017 #2
    Could you post image of your graph ?

    I am getting value of time which is slightly lesser than what you are getting .
    Last edited: Aug 3, 2017
  4. Aug 3, 2017 #3


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    Gold Member

    When you calculated the acceleration did you get a figure of -0.194444m/s^2. If so don't round it down to -0.19m/s^2 for the next step as that seems to account for your slightly different answer to the one I get.
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