1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Momentum and impulse?

  1. Jan 10, 2010 #1
    I'm a little confused about momentum and impulse.
    Its not a single problem but just how they relate.

    For example if a 2kg block moving at 3 m/s hits a 6 kg block,
    then it will move 1 m/s because momentum is conserved with
    6 momentos on either side of the equation. If the impact time is 1 millisecond
    whats the impulse? I dont know how you get impulse from momentos.
    Impulse is force x delta time and Momentum is mass x velocity, but in this problem
    how do i get impulse using the fact that the system's momentum is 6 momentos.
  2. jcsd
  3. Jan 10, 2010 #2
    What you have to understand is that Change in Momentum = Impulse, as described in the equation F delta T=m delta v. So in this case, it is not 6 momentos on either side, but 6 momentos combined because the initial Momentum must equal the final Momentum, which is the Momentum of both blocks added together.
    Last edited: Jan 10, 2010
  4. Jan 10, 2010 #3


    User Avatar
    Science Advisor
    Gold Member

    We have Newton's second law:


    This can be expressed as:

    Assuming the mass doesn't change. Now, if we integrate both sides with respect to time, we get the impulse I: (assume correct limits of integration)

    [tex]I=\int{Fdt}=\int{\frac{dp}{dt}dt}=\int{dp}=\Delta p = p_f-p_i[/tex]
    Therefore, the impulse is simply the change in momentum.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook