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Conceptual question about momentum, impulse, and average force.

  1. Apr 11, 2010 #1
    1. The problem statement, all variables and given/known data

    In a performance test two cars take the same time to accelerate from rest up to the same speed. Car A has a mass of 1400 kg, and car B has a a mass of 1900 kg. During the rest, which car:

    a)Has the greatest change in momentum?
    b)Experiences the greatest impulse?
    c)Is acted upon by the greatest net average force?

    2. Relevant equations
    P= mv
    Impulse= F(change in T)


    3. The attempt at a solution


    a) I think that car B has a greater change in momentum because momentum is the product of the velocity and mass, and car B has a greater mass which means the difference or CHANGE will be greater as well.

    b) I think the impulse will be the SAME for both cars because the problem states that it takes both cars the SAME time to accelerate and reach the same speed. Which means their force is the same. The fact that both cars have different masses does NOT play a role in the impulse. The fact that one car is heavier just means that the CAR will have to work harder to get the SAME acceleration as the lighter car.

    c) Both forces are the same I believe due to my explanation on part (b).
     
  2. jcsd
  3. Apr 11, 2010 #2

    PhanthomJay

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    part a is correct,but parts b and c are not. What is the equation for impulse in part b? The answer to part c should readily follow.
     
  4. Apr 11, 2010 #3
    Why is my logic incorrect? Why is your logic correct? Can you please explain? I have a test coming up and I am trying to grasp some conceptual questions:)
     
  5. Apr 12, 2010 #4

    PhanthomJay

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    You correctly answered part a by noting the definition of momentum. Now you need to note the definition of impulse, or better yet, write down Newton's 2nd law and examine it's concept. Also, if the heavier car has to work harder to achieve that acceleration and speed in the same time, this may help in part c as well.
     
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