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The work needed to move a mass of 5.41 kg 39.5 m

  1. Sep 29, 2016 #1
    1. The problem statement, all variables and given/known data
    The work needed to move a mass of 5.41 kg 39.5 m against a resistive force of 24.9 N is _____J.

    2. Relevant equations
    W = F x d

    3. The attempt at a solution
    F=ma
    Fapplied - Resistive Force = 5.41(a)
     
  2. jcsd
  3. Sep 29, 2016 #2

    Simon Bridge

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    Welcome to PF;
    ... please explain your reasoning, and remember to include units in the answer.
    I don't know what you mean by "(a)" in there. It looks like you are trying to calculate a force and you have noticed that you do not know the acceleration.

    The work is the magnitude of the applied force multiplied by the distance moved in the direction of the applied force.

    In the problem, you are told there is a "resistive" force - maybe that is the wind pushing on the object.
    In order to move the object "against the wind", what is the minimum applied force that is needed?
     
  4. Sep 29, 2016 #3
    It's hard for me to explain due to the question only being worded like that in my homework assignment.
    I meant 'a' as in acceleration. I am completely unaware of how to find the minimum applied force.
     
  5. Sep 29, 2016 #4

    Simon Bridge

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    You use Newton's laws of motion ... ##\sum F = ma## will do it.

    [edit: I am changing notation to better comply with PF rules...]
    Say, ##F## is the magnitude of the applied force, and ##f## is the magnitude of the resistive force, and take the +x direction as positive ... then:

    You already figured that ##F-f = ma## ... but you do not know the value of "a".
    You know the object has to be moving in the direction of ##F## (which is against ##f##)... so what is the smallest value of ##F## that does this?
    ie. If ##F = 1000f## ... which direction is the motion in? Is that the smallest ##F## can be?
     
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