The answer that the book gives for the question:(adsbygoogle = window.adsbygoogle || []).push({});

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?

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# Homework Help: Projectile Launch - Earth's Radius

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