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Homework Help: Newtons Laws?

  1. Sep 28, 2005 #1
    Newtons Laws??????????

    well i tied this prpblem
    you apply a force of .35 n [up] to a fork and it accelaraion is .15m/s^2 wats its mass in grams
    well i tried rearanging the force equation
    but i got the worng answer si i thoght i rearanged wrong so i tried swithing the varables but that stil didnt work so i figerd there must be another force the only on i can think of is gravty 9.8 m/s^2 [down] but they are on oppiste sides si i just need to know ehn adding vectors that are both horizantal do u still need to do a vector diagem and get their componants then solve or is there an esier way :confused: :confused:
  2. jcsd
  3. Sep 28, 2005 #2


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    Homework Helper

    You are on the right track. There are 2 forces acting in opposite directions. Why do you think you have it wrong?
  4. Sep 28, 2005 #3

    Try this!! First your error was that you are not converting the force(N), into grams remember that N= kg*m/s^2. So, what you really have is 350g*m/s^2. Then Newton's second law says F=m*a. So, what we do is we divide by the acceleration(a) both sides, as a result you will have m=F/a, the answer should be 2333g.
  5. Sep 28, 2005 #4
    the book answere was 35g
  6. Sep 28, 2005 #5

    Doc Al

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    Staff: Mentor

    It looks like you realize that two forces act on the fork: the applied force of 0.35 N acting upward, and the weight acting downward. Weight depends on mass according to the formula [itex]w = m g[/itex].

    If you take up as positive, then the net force will be the Applied force minus the weight. Set that equal to "ma" and solve for the mass.
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