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Homework Help: Help with Forces?

  1. Sep 9, 2012 #1
    An airplane has 1.50x10³ m to accelerate to a speed of 62.0 m/s to take off. If it experiences 15,000N of friction, calculate the thrust of the engines.

    d=1.50x10³ m
    vi=0 m/s
    vf=62.0 m/s

    a=1.2813 m/s²

    I think I'm supposed to find the applied force, but I don't know what to do next since I can't find the mass of the airplane.

    A 4.5kg axe comes to a stop in a tree from 25 m/s. How much force did the tree exert on the axe?

    I couldn't come up with anything for this one:

    u=25 m/s
    v=0 m/s
    m=4.5 kg

    Last edited: Sep 9, 2012
  2. jcsd
  3. Sep 9, 2012 #2


    User Avatar

    Staff: Mentor

    Both questions are missing critical information that would be needed to calculate a numerical answer. Thus the best you can do is to derive symbolic results with the missing information in the form of a variable. In the first case the missing information is the airplane's mass. In the second it's the depth of penetration of the axe into the tree (or perhaps the time for the axe head to come to rest).
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