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Homework Help: Magnitude of Net Force

  1. Mar 9, 2010 #1
    1. The problem statement, all variables and given/known data

    A 1200 kg pickup truck tows a small 300 kg trailer using a relatively lightweight tow rope. The position of the trailer is given in m and time in s. *There is an animation which shows the truck pulling the trailer across X-axis.
    Given: x= -20; y= +1 **BTW, i dont know what the given has to do with anything here! :x
    Starts from zero ends at 16 seconds.

    2. Relevant equations

    I know F= ma. They did not give acceleration so I looked up my notes and found that:
    if I set p=truck and r= trailer g=ground, then

    a = Fpg - Frg/ (mp + mr) ...... a= F/m

    3. The attempt at a solution

    but I'm not sure if I set that up right! I mean i took mass of truck (p) = 1200kg x 9.8 m/s^2 to give me 11760 N then mass of trailer (r) = 300 kg x 9.8 m/s^2 to give me 2940 N. (11760-2940/(1200+300) = 8820/1500 = a = 5.88.
    So if F= ma, then F = 1500 x 5.88 which gives me 8820 N.

    Is this correct? What should I do? Please help...physics scares me lol

    OK, so i know its incorrect bc I got it wrong on my online hw (webassign). So....?
    Last edited: Mar 9, 2010
  2. jcsd
  3. Mar 9, 2010 #2


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    Science Advisor
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    Gold Member

    You are going to have to clarify the problem. Does the truck-trailer system travel 20 meters in 16 seconds? You'd have to calculate the acceleration, then the net force providng that acceleration. Welcome to PF.
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