1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Force (Newtons Laws of Motion)

  1. Jul 9, 2009 #1
    1. The problem statement, all variables and given/known data
    For a birthday gift, you and some friends take a hot-air balloon ride. One friend is late, so the balloon floats a couple of feet off the ground as you wait. Before this person arrives, the combined weight of the basket and people is 1220 kg , and the balloon is neutrally buoyant. When the late arrival climbs up into the basket, the balloon begins to accelerate downward at 0.59m/s2 .What was the mass of the last person to climb aboard?


    2. Relevant equations
    F=ma



    3. The attempt at a solution
    do I need to find the net force before and after the last person's arrival?then compare those 2 equations to get the last person's mass? could somebody give me a clue how to approach this kind of a problem?

    Thanks in advance.
     
  2. jcsd
  3. Jul 9, 2009 #2

    rock.freak667

    User Avatar
    Homework Helper

    On the air balloon there are two forces, weight (downwards) and upthrust (upwards) .

    So yes, you need to compare before (which will give you the upthrust) and then after to get the person's mass.
     
  4. Jul 9, 2009 #3
    so would the 1st equation be??
    upthrust (F_u) - Wt of the basket & people (W) = mass (m). acceleration (a)
    F_u - 1220 * 9.81 = 1220 * 0.59
    Therefore F_u = 12919.8 N

    would the 2nd equation be??
    F_u - (1220+mass of last person)g = (1220+mass of last person)a

    am I in right way ........??? if not could you please help me?

    Thanks again...
     
  5. Jul 9, 2009 #4

    rock.freak667

    User Avatar
    Homework Helper

    I think [itex]F_U -W =0[/itex] since before the other person jumps into the basket it is just hovering. The second equation is correct.
     
  6. Jul 10, 2009 #5
    The first equation is Fu-Wt=0 ,because at the beginning the acceleration is zero, because "the balloon is neutrally buoyant" at the beginning.
     
    Last edited: Jul 10, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Force (Newtons Laws of Motion)
Loading...