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: Elastic collision.

  1. Nov 23, 2008 #1
    1. The problem statement, all variables and given/known data

    A 70kg man who is ice skating north collides with a 30kg boy who is ice skating west. Immediately after the collision, the man and boy are observed to be moving together with a velocity of 2m/s in a direction 37 degrees north of west. What was the magnitude of the boy's velocity before collision.
    2. Relevant equations

    3. The attempt at a solution
    I do not really know where to start. Could someone please list equations that are needed for this problem.
  2. jcsd
  3. Nov 23, 2008 #2
    i meant to title inelastic
  4. Nov 23, 2008 #3
    use conservation of momentum, you should have an equation for the y axis (north/south) and an equation for the x axis (east/west)
  5. Nov 23, 2008 #4
    I do not see how to use it when only the final velocity is given.
  6. Nov 23, 2008 #5
    ok im not sure if this is right, but i made the equation m2v2cos=m1v1'cos+m2v2'cos
    and found v2 to equal 2.13 would that be my final answer?
  7. Nov 23, 2008 #6
    usually good to break these down into momentum in x direction and y direction

    M_{man}V_{man} \hat{y} = M_{final}V_{yfinal} \hat{y}
    M_{boy}V_{boy} \hat{x}=M_{final}V_{xfinal} \hat{x}
    M_{final} = M_{boy} + M_{man}
    V_{yfinal} = \left( 2 \frac{m}{s} \right) cos(37^{\circ})
    see if you can determine the other final V and solve, lemme know if you have questions on notation and such
    Last edited: Nov 23, 2008
  8. Nov 23, 2008 #7
    Thanks im good now
  9. Nov 23, 2008 #8

    "may entropy increase in a way that favors your sword"
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook