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Homework Help: Force and Air Balloon problem help

  1. Jan 16, 2012 #1
    1. The problem statement, all variables and given/known data
    A hot-air balloon consists of a basket, one passenger, and some cargo. Let the total mass be M. Even though there is an upward lift force on the balloon, the balloon is initially accelerating downward at a rate of g/3.

    The passenger notices that he is heading straight for a waterfall and decides he needs to go up. What fraction of the total weight must he drop overboard so that the balloon accelerates upward at a rate of g/2? Assume that the upward lift force remains the same.

    Lift Force = 2Mg/3

    2. Relevant equations
    F = ma

    3. The attempt at a solution
    I basically just tried to divide 2Mg/3 with g/2. But I just got M(4/3). The answer is 5/9. What critical information am I missing?
  2. jcsd
  3. Jan 16, 2012 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    To start, apply that equation to the situation where the balloon is accelerating downward at g/3. What do you get? (You might need to think carefully about what the F means in F=ma.)
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