# Calculating Escape Velocity

How do you Calculating the escape velocity? I googled it but they give bad instructions on how to do it. What is the formula?

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Every time I try using the formula i have i have to solve for V^2 and I get it to equal 35
3541. Is this right? I plug in the numbers like it says it I still dont get the right answer.

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mgb_phys
Homework Helper
Gravitational potential energy is = GMm/r (where M is the mass of the earth)
Kinetic energy = 1/2 m v^2

You start at r=radius of earth and end up at r=infinity.
A bit of rearranging and a subtraction and it shoudl be easy

I set KE=GPE i get a velocity of 465,561 for a 10kg object. This doesnt seem right.

Nabeshin
I set KE=GPE i get a velocity of 465,561 for a 10kg object. This doesnt seem right.
Well escape velocity is a function of radius so this question, as you stated, makes no sense...

Janus
Staff Emeritus
Gold Member
Every time I try using the formula i have i have to solve for V^2 and I get it to equal 35
3541. Is this right? I plug in the numbers like it says it I still dont get the right answer.
What formula are you using?

What formula are you using?

V$$^{2}$$=$$\frac{2GM}{R}$$ to find the escape velocity of the earth and i get, 465561.808.

sylas
$V^{2}=\frac{2GM}{R}$ to find the escape velocity of the earth and i get, 465561.808.
You've got "tex" tags inside your formula. I've tried to fix tags in the quoted extract; but it is still not displaying for some reason. But the forumla looks fine to me. Just make sure all your variables are in consistent units. You give a number, but no units. Are you meaning km/hr, or m/s, or something else?

The gravitational constant G is usually given in SI units. If you do everything in meters and seconds and kilograms, it will work.

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Janus
Staff Emeritus
Gold Member
Every time I try using the formula i have i have to solve for V^2 and I get it to equal 35
3541. Is this right? I plug in the numbers like it says it I still dont get the right answer.
Okay, from this answer, I'd say that you are using kilometers instead of meters for the radius of the Earth.

mgb_phys