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Homework Help: Projectile please help

  1. Mar 20, 2006 #1
    This is a follow from a post i made yesterday. The question is:

    2 particles are projected vertically up one after another from the same point at same initial speed u. T is the time interval between the 2 projections, where T<2u/g. Find what further time elapses before the particles collide, and find their speeds immediately before impact.

    The equations i have found so far are for distance travelled
    x= -0.5gt^2 + ut.
    However i have realised this formula is for the distance the particle has travelled rather then the height reached. Since i need to find the time when the particles will collide (ie when they are at the same height) i am stuck as i think the formula is no use?! Please help
  2. jcsd
  3. Mar 20, 2006 #2
    Hint : x is not actual distance but displacement.
    Can u go from here?
  4. Mar 20, 2006 #3
    so i should equate the equations for x for both particles? how would i substitute T into the equation for particle 2?
  5. Mar 20, 2006 #4
    Yes u should equate x.

    Take t as time for first proj. and t-T for second proj.
    Solve for t in terms of T.
  6. Mar 20, 2006 #5
    ok thats great thanks for your helpx
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