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Kinematics with multiple objects

  1. Oct 15, 2011 #1
    1. The problem statement, all variables and given/known data
    Mike is standing below a tower. His friend on top of the tower which is 580 m drops a ballon at him. At the instant mike fires a potato from a cannon moving at an initial velocity of 95 m/s. How long does it take for the ballon and potato to collide?


    2. Relevant equations
    vf=vi+at
    vf^2=vi^2+2ax
    x=vi*t+0.5at^2
    x=0.5(vi+vf)t


    3. The attempt at a solution
    What i did is split it into 2 parts one for the ballon and potato. The potato equation was
    x=95t+0.5(-9.81)t^2
    And the ballon equation as
    x=0.5(9.81)t^2
    and then i set them equal to each other and solved.
    I got t=9.684 s
    1. The problem statement, all variables and given/known data
    Two cars initially 1 km apart are traveling towards each other. If Car A is travelling at 80 km/h east constantly and Car B accelerates at a rate of 10m/s^2 from rest. When will they pass each other and where?


    2. Relevant equations
    vf=vi+at
    vf^2=vi^2+2ax
    x=vi*t+0.5at^2
    x=0.5(vi+vf)t



    3. The attempt at a solution
    I tried the same idea as i did before and got 22.2t=5t^2 and then t=4.44s and then i tried a different method by using systems of equations.
    x=1000-10t
    t=1000/22.2
    subbed 1 into 2 and got 549.55m then subbed that into x=vi+0.5at^2 and got t=10.48s
     
  2. jcsd
  3. Oct 15, 2011 #2

    PhanthomJay

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    Science Advisor
    Homework Helper
    Gold Member

    For each problem. splitting into 2 parts is good, but you should note that the distances traveled in each part are not the same. For the potato problem, the balloon travels y meters and the potato travels (540-y) meters when they hit. Similarly, for the car problem, if car A travels x meters , car B travels (1000 - x) meters when they meet.
     
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