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Homework Help: Breaking Plates

  1. Oct 29, 2004 #1
    Q. While thinking about your physics homework, you drop one of your mom's dinner plates on the floor breaking it into three pieces. The second piece has a mass of 2 times the first piece and flys off perpendicular to it. These first two pieces both have a speed of 2.6 m/sec. The third piece has 3 times the first piece.

    a) What is the magnitude of the velocity of the third plate?
    For this I applied consevation of momentum in both the x and y directions, and got the answer, which is correct.

    Take the direction of the first piece to be the x axis, the direction of the second piece to be the y axis, and angles to be measured positive counter-clockwise from the x axis.
    b) What is the direction of the third plate?

    I tried to find the direction using , tan theta = v3y / v3x, but still the computer says the answer is incorrect. Is the idea correct.

    For this portion of the problem, assume the plate had a total mass of 1.4 kg.
    c) What was the total impulse delivered to the third piece?

    J3 = ? I know that impulse is the change in momentum Delta P, which is

    p2 - p1, but how do I apply it in this situation.

    Please help, Thanks!
  2. jcsd
  3. Oct 29, 2004 #2


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    b) Your method seems correct. I can't say more unless I see exactly what you have done.

    c) I guess what you want here is the change in momentum along the final direction. Since the initial momentum along this direction = 0. The final momentum should be the required answer.
  4. Oct 30, 2004 #3
    But how would I find m3, the total mass is 1.4 kg.
    and m3 = 3m1
    m2 = 2m1
    v1 = 2.6 m/s

    v2 = 2.6m/s

    Would the above info help us in solving this problem , if so , what would the final eqn, look like.

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