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Equation for velocity

  • #1
i was working on a differential equation to find the initial velocity of a rocket to get to height h.

so i have, which i got and its correct cause its the solution in the book, v^2 = 2g(R/(R+h))-2gR+V(0)^2

v = velocity
g = acceleration of gravity at earths surface
R= radius of earth
h = height
and i assume v(0) is the velocity v at height=0 so v(0)=0?

Problem is when i keep getting a negative number. so i assume I'm making an amateur mistake.

What am i doing wrong? ive tried converting etc. im using km
 

Answers and Replies

  • #2
rude man
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i was working on a differential equation to find the initial velocity of a rocket to get to height h.

so i have, which i got and its correct cause its the solution in the book, v^2 = 2g(R/(R+h))-2gR+V(0)^2
Really? I'm concerned because the terms in your equation don't match dimensions. Specifically, 2gR/(R+h) does not match 2gR.

Make that very concerned. :uhh:
 
  • #3
I'm trying to use this
diff-eqn-rocket.jpg

y = R (the radius of the earth) +h ( the height i want to reach).
 
  • #4
rude man
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The last equation looks OK except there's a minor typo in it. The equation before that is OK, so use it to solve for v0.
 
  • #5
whats the typo?
 
  • #6
rude man
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whats the typo?
Bottom equation, " v2 = v2 ". Equating velocity with velocity-squared is a no-no.
 

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