Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: A plane

  1. Oct 16, 2004 #1
    My question is as follows..."An airplane flies in a loop(a circular path in a

    vertical plane) of radius [tex]150m[/tex]. The pilot's head always points

    toward the center of the loop. The speed of the airplane is not constant, the

    aiplane goes slowest at the top of the loop and fastest at the bottom. a) At

    the top of the loop, the pilot feels weightless. What is the speed of the

    airplane at this point?"

    Since the speed is not constant I would use the formula[tex]\sum{\vec{F}}

    =m\vec{a}[/tex]. I then drew a free body diagram, and there were no

    horizontal forces and the only vertical force was the weight. So I did this

    [tex]\sum{F_x}=ma_x=0[/tex] and for the y component [tex]\sum{F_y}

    =ma_y[/tex] since I chose from [tex]0[/tex] and up to be posative on my y

    axis i made weight =negative [tex]-mg=m\frac{v^2}{R}[/tex] then I

    multiplied both sides by [tex]\frac{R}{m}[/tex] the [tex]\frac{-mgR}{m}

    =v^2[/tex] and then [tex]m[/tex] cancels out and [tex]-v=\sqrt{gR}[/tex]

    I think I choose a bad axis system...my answer is the correct

    magnitude but...theres that negative sign lurking about... :bugeye: Is it bad

    algebra or a bad cordinate system?
  2. jcsd
  3. Oct 16, 2004 #2
    Which way does the centripetal force point?
  4. Oct 16, 2004 #3
    twords the [tex]-x[/tex] axis
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook