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Homework Help: Calculating Force with Mass and Acceleration

  1. Oct 6, 2012 #1
    1. The problem statement, all variables and given/known data
    Mass= 36.1 (Grams)
    Acceleration = 1.36 M/S(sqaured)
    Net Force in Milinewtons =

    2. Relevant equations
    Fnet= MA

    3. The attempt at a solution
    Fnet= 0.0361 x 1.36
    = 0.049096 Newtons
    0.049096 x 1000= 49.096 Milinewtons

    Can anyone verify this for me please?
    Last edited: Oct 6, 2012
  2. jcsd
  3. Oct 6, 2012 #2


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    Hi, socialfox.

    Your work look's good. (Picky: If the problem is stated with 3 significant figures for each quantity, then generally you would round your answer to three significant figures: 49.1 mN.

    Also, "milli" has two l's.
  4. Oct 6, 2012 #3
    Thank you for replying, I had another question with that information I was supposed to calculate the force of resistance with this equation:

    9.8(Mass)(Sin*angle*) - (m)(a)
    so I had filled it in with these numbers below (the angle is 10.4 degrees)

    9.8(36.1)(sin10.4) - 49.096 = 14.768 MilliNewtons
    I understand this answer seems normal but for another question with simmilar numbers except for the degrees which is now 11.24 degrees I get this

    9.8(36.1)(sin11.24) - 68.951 = 0.000749325 MilliNewtons

    My problem/doubt is why is my second answer so different, also is the force of resistance correct for these questions?

    Thanks for taking the time to look over this, I appreciate it :)
  5. Oct 6, 2012 #4


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    Your calculations look correct. However, I think it would be more consistent if you plug in SI units (.0361 kg) for the mass and then convert Newtons to milliNewtons. But' you'll get the same result.

    The results seem so different because in the last case you happen to be subtracting two terms that have almost the same value.

    It's hard for me to say if your "force of resistance is correct" since I don't know the set-up of the problem. Maybe you could explain how you arrived at the expression mgsinθ - ma.
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