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Homework Help: Force and finding mass.

  1. Oct 30, 2007 #1
    1. The problem statement, all variables and given/known data

    A Constant force of 75 N is applied horizontally to a block of ice on a horizontal plane. Friction is negligible. The block moves 12 m in the first 3 seconds. Find Mass in kg of block.

    2. Relevant equations



    3. The attempt at a solution

    Having trouble finding acceleration. I took 12m/3s to find the velocity, then velocity over time to give acceleration. I came up with 1.3 but this appeared to be incorrect. Help with the proper finding of acceleration would be great.
  2. jcsd
  3. Oct 30, 2007 #2
    is the answer 28.12 Kg?
  4. Oct 30, 2007 #3


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    Homework Helper

    If the block starts from rest, the initial velocity is zero. So if you know the distance, time and initial velocity, which kinematic equation will give you acceleration?
  5. Oct 30, 2007 #4
    Ahh yes it is, could you tell me what you did to get the acceleration?
  6. Oct 30, 2007 #5
    Ahhh I didn't even look at the kinematic equations. I will do that.
  7. Oct 30, 2007 #6
    If it starts from rest you know:

    - V1=0
    - V2=?
    - Displacement=12m
    - Time=3s

    To get V2 we use the equation that relates all our known variables. This equation is; Delta D={(v1+v2)/2}* Delta Time

    After you find V2 use the equation A= (V2-V1)/Delta Time to find acceleration. From there plug A into Fnet=ma and find mass.
    Last edited: Oct 30, 2007
  8. Oct 30, 2007 #7
    Awesome, that all works, thanks :)
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