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Homework Help: Can I find time without knowing initial velocity?

  1. May 19, 2012 #1
    1. My problem is I know displacement is 20m, acceleration is -5.4m/s, final velocity is 0m/s, coefficient of friction=0.55, the object slowing down weighs 1000kg, can I find initial velocity and the time it took to slow down and if so how? I have no idea how to go about this problem

    2. Equations of motion and coeffcient of friction = frictional force/normal force?? maybe F=ma

    3. As I said I really dunno how to start this one or if its even possible at my level.
  2. jcsd
  3. May 19, 2012 #2
    Do you have a formula that relates final velocity to initial velocity plus an acceleration-distance term?

    You can also do this problem with work-energy relationships if you've studied that.


    Take the usual equation: d=V0*t+.5*a*t^2 and eliminate the variable t by inserting the relationship between final velocity, acceleration, and time. Solve for final velocity.
  4. May 19, 2012 #3
    I woke up this morning, looked at this and it all jsut clicked in my head thankyou.
  5. May 19, 2012 #4
    Is the initial velocity 14.7 m/s^2?
  6. May 20, 2012 #5
    That's it.
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