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Homework Help: 2-dimensional impuse

  1. Oct 26, 2007 #1
    A ball of mass 7.0 g with a speed of 25.2 m/s strikes a wall at an angle 23.0 ° and then rebounds with the same speed and angle. It is in contact with the wall for 39.0 ms. What is the magnitude of the impulse associated with the collision force?


    x: -mv*sin(23)-mv*sin(23)
    y: -mv*cos(23)+mv*cos(23)=0

    I'm not sure what I did wrong, but I got -137.85, and the magnitude is 137.85/
  2. jcsd
  3. Oct 26, 2007 #2


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    Magnitude of a vector is positive, while the + or - determines direction, as in +x, -x or +i, -i.
  4. Oct 27, 2007 #3
    I'm pretty sure my free body diagram is right. I'm not too sure what I'm doing wrong. The computer isn't taking that answer.
  5. Oct 27, 2007 #4
    I know that both of the vectors are in the negative x direction, and one is in the positive, and the other is in the negative y direction.

    I realized that I forgot to convert to kilograms, however, the answers is still wrong:

    I got.2098
    Last edited: Oct 27, 2007
  6. Oct 27, 2007 #5


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    I noticed the grams think, but I though it was a typo. That said how can you convert 137.85g*m/sec to kg and get .2098?
  7. Oct 27, 2007 #6
    Oh, I converted the g to kg at the very beginning. 7g=.007kg

    so my equation looked like this

    x=-.007*25.2*sin(23)+-.007*25.2*sin(23)=.2098 N*s
    Last edited: Oct 27, 2007
  8. Oct 27, 2007 #7


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    I'd try that again. I get something different. You are doing sin(23) in degrees, yes?
  9. Oct 27, 2007 #8
    yes, are my numbers in the equation correct.
  10. Oct 27, 2007 #9
    Okay, I modified my equation and only did the first half of it and got .0698, I multiplied that by 2 and got the right answer. I must have committed an algebra error somewhere.
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