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!

Impulse/final velocity question confusion

  1. Jul 8, 2015 #1
    I uploaded my question below; basically I am confused in part b) where they show that:
    50 kgm/s = (5kg)v2 - (5kg)(-4m/s) then they say that
    30 kgm/s = 5kg v2, but shouldn't it be 70 kgm/s = 5kg v2?

    As noted at the beginning of the question North is positive and thus since the cart moves south is negative (-4m/s).
    Could this be a typo ?
     

    Attached Files:

    • hw.PNG
      hw.PNG
      File size:
      37.5 KB
      Views:
      83
  2. jcsd
  3. Jul 8, 2015 #2
    If south is negative and that was the initial direction of momentum then the second term is written correctly. Note carefully the signs (subtracting a negative on the RHS) so the second line is correct because the equation reads (without units) 50 = 5v + 20.
     
  4. Jul 8, 2015 #3
    yeah I totally missed the subtracting a negative on the RHS that makes more sense now thank you
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...