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Escape speed

  • Thread starter imy786
  • Start date
  • #1
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Homework Statement



By considering the gravitational potential energy of an object at the surface , find an expression for the escape speed from the surface and determine its value.

Homework Equations



GPE= mgh

The Attempt at a Solution



KE= 1/2* m * v^2

GPE= mgh

GPE+ KE = 0

mgh = - 1/2 * m * v^2
gh= - 1/2 * v^2


v^2= -2gh

v= sqare root of (-2gh)

this is the escape velocity...
 

Answers and Replies

  • #2
Dick
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You've computed velocity needed to reach a height h in a uniform gravitational field. Is that the same concept as 'escape velocity'?
 
  • #3
HallsofIvy
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You also appear to be assuming gravitational force is constant. If that were true, there would be no "escape velocity". It is impossible to "escape" a constant force!
 
  • #4
Well if ur looking for escape velocity....it should be[tex]\sqrt{\frac{2GM}{R}}[/tex]
 
  • #5
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thanks for the info...
so how shall i start off instead
 
  • #6
you shud use the work energy theorem
 
Last edited:
  • #7
Dick
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You should change your expression for gravitational potential energy to one appropriate for a nonconstant field.
 
  • #8
HallsofIvy
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Remember that gravity is an "inverse square formula"!
 

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