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Momentum problems

  1. Dec 17, 2012 #1
    1. The problem statement, all variables and given/known data
    A 2000 kg truck is moving at a speed of 30 m/s. It hits a haystack and stops in 80m.
    1a. What is the original momentum of the truck?
    1b. What is the final momentum of the truck?
    2a. What is the original kinetic energy of the truck?
    2b. What is the final kinetic energy of the truck?

    I'm not sure how to do these, and I've started some, but stuck on the last two. Also, am I correct in assuming final velocity to be 0 m/s?

    2. Relevant equations
    m1v1i + m2v2i = m1v1f + m2v2f
    (1/2)m1v1i2 + (1/2)m2v2i2 = (1/2)m1v1f2 + (1/2)m2v2f2
    P=mv
    3. The attempt at a solution
    1a. P=mv
    P=(2000 kg)(30m/s)= 60,000 kg x m/s

    1b. P=mv
    P=(2000kg)(0 m/s) = 0 kg x m/s
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 17, 2012 #2

    SammyS

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    You have done 1a & 1b correctly.

    Do you know how to calculate kinetic energy?
     
  4. Dec 18, 2012 #3
    The initial kinetic energy of the truck is 900,000 kg x m/s? that seems wrong.. but the final should be 0, since final velocity would be 0 m/s.
     
  5. Dec 18, 2012 #4

    haruspex

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    kg x m/s is wrong certainly. The number is right if you meant kg m2/s2 (better known as Joules). Why did it seem wrong?
     
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