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Homework Help: Impulse question

  1. Nov 15, 2008 #1
    1. The problem statement, all variables and given/known data
    A ball of mass 0.4 kg is initially at rest on the
    ground. It is kicked and leaves the kicker’s
    foot with a speed of 5.0 m/s in a direction 60◦
    above the horizontal.
    The magnitude of the impulse k~Ik imparted
    by the ball to the foot is most nearly:

    1. ||J|| = 1Ns.
    2. ||J|| =(2/√3) Ns.
    3. ||J|| = 2Ns.
    4. ||J|| = 4Ns.
    5. ||J|| = √3 Ns.

    2. Relevant equations
    J = Ft = change in p

    3. The attempt at a solution
    I figured the angle didn't matter in this situation since the impulse would be in the same direction as the velocity...

    So using
    J = mvf - mvo
    J = 0.4 kg (5.0 m/s) - 0.4 kg(0 m/s)
    J = 2 Ns

    Did I do this correctly?
  2. jcsd
  3. Nov 15, 2008 #2


    User Avatar

    Yes, from Newton's second law the impulse equals the change in momentum as you write which gives the answer you provide.

    Your thoughts on the indifference of the angle it is correct, you can think of it as that the impulse has "nowhere else to go" but the foot.
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