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Homework Help: Linear Momentum - Checking quick questions

  1. Mar 16, 2007 #1
    What is the SI unit of momentum? --> N x s

    When a light beach ball rolling with a speed of 6.0 m/s collides with a heavy exercise ball at rest, the beach ball's speed after the collision will be, approximately? --> 6.0 m/s

    In an inelastic collision, if momentum is conserved, then which of the following statements is true about kinetic energy? --> Kinetic energy is lost.

    Which of the following is an accurate statement?
    The momentum of a projectile is constant. <---
    The momentum of a moving object is constant.
    If an object is acted on by a non-zero net external force, its momentum will not remain constant.
    If the kinetic energy of an object is doubled, its momentum will also be doubled.

    A 4.0 N force acts for 3.0 s on an object. The force suddenly increases to 15N and acts for one more second. What impulse was imparted by these forces on the object? --> 16.3 N·s

  2. jcsd
  3. Mar 16, 2007 #2
    I can't figure out how to find the impulse without mass...
    Last edited: Mar 16, 2007
  4. Mar 16, 2007 #3
    1 and 2 are correct.

    For #3, the answer is a bit ambiguous. All KE need not be lost.

    #4 - Wrong. Hint: Newton's 1st law.

    #5 - How did you get 19? What's the definition of impulse?
  5. Mar 16, 2007 #4
    For #3:
    If an object is acted on by a non-zero net external force, its momentum will not remain constant.
    This seems to comply with the 1st law.
  6. Mar 16, 2007 #5
    Impulse is what changes the momentum of an object.. right?
  7. Mar 16, 2007 #6
    Don't worry about it, I'll ask the teacher.

  8. Mar 16, 2007 #7
    Right. So is a projectile free of non-zero net external forces?

    Well, not exactly. Force is what changes momentum. Impulse is change in momentum(in a certain time interval).

    [tex]J = F\Delta t = \Delta p[/tex], for a constant force F. J is impulse, btw.
  9. Mar 16, 2007 #8
    Now you tell me! :grumpy: :biggrin:
  10. Jan 19, 2011 #9
    i just cant comprehend getting the impulse without mass.
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