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Homework Help: Mass, speed, and force to find new speed and distance traveled during period.

  1. Jan 27, 2013 #1
    . The problem statement, all variables and given/known data

    A train has a mass of 5.77E+6 kg and is moving at 99.4 km/hr. The engineer applies the brakes, which results in a net backward force of 1.11E+6 N on the train. The brakes are held on for 26.9 s.

    What is the new speed of the train?

    How far does it travel during this period?

    mass of train: 5,770,000 kg

    speed of train: 99.4 km/hr (i converted it to m/s and got 27.611 m/s)

    Backwards net force of: 1,110,000 N

    Brakes held for: 26.9 s

    2. Relevant equations




    3. The attempt at a solution

    I am fairly new to physics and don't really know what I'm doing, anyways...first i used f=ma
    and got a=.192 then i used that in the second equation and got V=1,110,005.165 N and then I plugged that into the third equation and got 29859069.4666 M but it said i was wrong :/.

    I am not asking for the answer, just what equations to use and what order to do what in, of coarse if you would like to solve it for me feel free:)

    -Thanks in advance!
    Last edited by a moderator: Jan 27, 2013
  2. jcsd
  3. Jan 27, 2013 #2


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    2017 Award

    Staff: Mentor

    Try to work with units, it helps spotting errors in your calculations.
    Your 3 equations are correct, and can be used to solve the problem.

    V in your second equation is a velocity, not a force.
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