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Homework Help: One and Two Dimension collisions

  1. Nov 7, 2006 #1
    My question is not so much what to do it is just i have problems solving for a certain equation.

    A 5.00kg ball, moving to the right at a velocity of 2m/s on a frictionless table, collides head-on with a stationary 7.50kg ball. Find the final velocities of the balls if the collision is (a) elastic and (b) completely inelastic

    for part A

    I have m1v1f + m2v2f= m1vi1 +0
    to solve for final velocity 1(the ball for 5kg) you use

    vf1=(m1-m2/m1+m2)vi1

    I really have no i do how to algebraically solve for vf1, can someone explain that to me because when i use the equation i get the right answer which is -.400m/s

    To find vf2 we use the fact that it is an ellastic collision and the kinetic energy before and after is the same

    1/2m1(vf1^2)+1/2m2(vf2^2)=1/2m1(vi1^2)+0
    Using this i have to solve for vf2 but again i have a problem algebraically solving for vf2. But there is a similar example in the textbook so i used what they had to solve for vf1 and vf2 but they do not show the work

    vf2=(2m1/m1+m2)vi1
    answer should be 1.60m/s

    Same problem here but the answers come out correctly.
    It would be greatly appreciated if someone can show me the algebra behind this
     
  2. jcsd
  3. Nov 7, 2006 #2

    radou

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    Homework Helper

    For (a): use the fact that both kinetic energy and momentum are conserved. This will give you two equations with two unknowns, which are the final velocities.

    For (b): what are the properties of a completely inelastic collision?
     
  4. Nov 7, 2006 #3
    I understand that but i need someone to show me how to algebraically solve for those two equations thats what my problem is i understand how to solve for the final velocities. Like show the math workout step by step because i am confused.
     
  5. Nov 8, 2006 #4

    radou

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    Homework Helper

    Here, take a look at: http://www.webmath.com/solver2.html" [Broken].
     
    Last edited by a moderator: May 2, 2017
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