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Homework Help: Three equations of motion problem

  1. Oct 25, 2008 #1
    1. The problem statement, all variables and given/known data
    Ball A is released from rest at height h1 at the same time that a
    second ball B is thrown upward from a distance h2 above the
    ground. If the balls pass one another at a height h3 determine the
    speed at which ball B was thrown upward.
    h1 = 40 ft
    h2 = 5 ft
    h3 = 20 ft
    g =32.2 ft/sc2

    2. Relevant equations
    the equation to be used are the three equations of motion, as the acceleration is constant.

    3. The attempt at a solution
    I couldnt attempt the solution becuase I am stuck a every equation as therer are many unknowns for ball B. WHat I can not find out yet is the relation between ball A and Ball B when they pass each other. There has to be property common in both at that time so that I can solve for B then. But again, after a lot of thinking I dont get how to do it still. Couldn't make any logic. The distance traveled is already given. Time taken and velocity will not be the same. What then?
  2. jcsd
  3. Oct 25, 2008 #2
    Re: Dynamics

    The "properties" that will be the same are the height and the time. They will be at the same height at the same time. But the problem is actually much simpler. You know where they meet so you can find the time from the equation for ball A and then plug into the equation for ball B.
    By equations here I mean equations of motion (height versus time).
  4. Oct 26, 2008 #3
    Re: Dynamics

    My confusion is that why will they take same time to meet each other? Like ball A can be at the meeting ponit in 5 secs while ball B can be there in 3 secs. I mean isn't it supposed to be dependent on their speeds ? How can we say here that they will meet each other at same time?
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