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Not hard If you know how (homework) I don't

  1. Mar 13, 2005 #1
    Does anyone out there have a few minutes to review a problem I worked out ?

    I need to know where I am making errors and how to correct them

    If you have a few minuted and are willing to help a fella out please reply ASAP

    Here goes The problem states to find the following
    1. Acceleration 5. Work
    2. mass 6.the weight of three rayovac cells placed on the object
    3. Force 7. momentum with and without cells
    4. KE 8. Impulse upon collision

    Trial 1 weight of object = 985.5 g .986 kg
    Xi = 100cm ti = 0
    Xf = 38cm tf = 4sec

    I need velocity for accelartion v = d/ t = -.62 m/4s = -0.155 m/s

    a = v / t = (0.155 m/s) / 4 s = -0.039 m/s^2

    mass = w / g = 0.986kg / (9.8 m/s^2) = 0.101kg (why is ans. not in newtons)

    Force F = m x a =0.101kg x (-0.039 m/s^2) = - 2.59 N

    KE = (1/2) m x v^2 = (1/2)(0.101kg)(-0.155 m/s)^2 = -0.024 J, (can J be -)

    work W = (F cos 0) X = ? I am stuck here, the object is on a level surface I am thinking that (cos 90) is correct am I right ?
    PLease any help will be appreciated I am trying to complete assignment and study for test. :eek:
     
  2. jcsd
  3. Mar 13, 2005 #2
    I see that this post is being viewed but not answered,

    Did I do something wrong or is there an error in the post

    I could really use a little help with this problem

    Is there anyone out there just make a post if you can read me is there anyone at home :surprised
     
  4. Mar 13, 2005 #3

    dextercioby

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    Homework Helper

    Okay.What's the text of the problem...?

    Daniel.
     
  5. Mar 13, 2005 #4
    [tex]W=Fdcos(\theta)[/tex]
    if the force is being applied horizontally, then [tex]\theta[/tex] would be zero

    Work is force times distance times cos(theta). In this case, if the force is being applied horizontally, then theta=0 so... cos(0)=1 so work would just be W=F*d
     
  6. Mar 13, 2005 #5
    :cry: Thank you
    The problem was an experiment done in class, it is set up as a collision between two cars on a track. one stationary and one propelled by a fan.
    Xi = 100cm, Xf = 38cm, ti = 0, tf =4s the rest of the problem is in my first post. If you need any further info let me know I will check back every few minutes. I am trying to figure out some other problems.

    Thanks again
     
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