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!

Projectile Launch - Earth's Radius

  1. Mar 21, 2005 #1
    The answer that the book gives for the question:
    What is the launch speed of a projectile that rises above the Earth to an altitude equal to the Earth's radius? Ans. 7.91 km/s

    Now I have the question:
    What is the launch speed of a projectile that rises above the Earth to an altitude equal to three times the Earth's radius?

    So I use:
    [tex]v_{f} = \sqrt(((2GM_{e})/(4R_{e}))[/tex]

    Note:
    G = 6.67x10^-11
    Me = 5.97x10^34 kg
    Re = 6.37x10^6 m

    The resulting answer I get is 5.59 km/s. That equation works for an altitude equal to the earth's radius, but not for my problem. Why not? What am I doing wrong?
     
  2. jcsd
  3. Mar 21, 2005 #2
    Possibly using 4R_{e} instead of 3R_{e}?
     
  4. Mar 21, 2005 #3

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The correct energy equation is:

    [tex]KE = \Delta PE = GMm(\frac{1}{R_{i}}-\frac{1}{R_{f}})[/tex]

    [tex]v_i= \sqrt{2GM(\frac{1}{R_e}-\frac{1}{4R_e})}[/tex]

    BTW, the mass of the earth is 5.97x1024 kg.

    AM
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Projectile Launch - Earth's Radius
  1. Launched projectile (Replies: 2)

  2. Projectile Launching (Replies: 4)

Loading...