A new planet has been discovered and given the name Planet X . The mass of Planet X is estimated to be one-half that of Earth, and the radius of Planet X is estimated to be twice that of Earth. The estimated mass and radius of Planet X are used to calculate the minimum escape speed, vc , for an object launched from the surface of the planet. If the actual mass and/or radius of the planet are slightly different from the estimated values.

Required:
How will the actual escape speed va for the surface of Planet X compare to vc?

Respuesta :

Answer:

    vₐ = v_c  [tex]( \ 1 + \frac{1}{2} ( \frac{\Delta M}{M} - \frac{\Delta R}{R}) \ )[/tex]

Explanation:

To calculate the escape velocity let's use the conservation of energy

starting point. On the surface of the planet

          Em₀ = K + U = ½ m v_c² - G Mm / R

final point. At a very distant point

         Em_f = U = - G Mm / R₂

energy is conserved

           Em₀ = Em_f

           ½ m v_c² - G Mm / R = - G Mm / R₂

           v_c² = 2 G M (1 /R -  1 /R₂)

if we consider the speed so that it reaches an infinite position R₂ = ∞

           v_c = [tex]\sqrt{\frac{2GM}{R} }[/tex]

now indicates that the mass and radius of the planet changes slightly

            M ’= M + ΔM = M ( [tex]1+ \frac{\Delta M}{M}[/tex] )

            R ’= R + ΔR = R ( [tex]1 + \frac{\Delta R}{R}[/tex] )

we substitute

           vₐ = [tex]\sqrt{\frac{2GM}{R} } \ \frac{\sqrt{1+ \frac{\Delta M}{M} } }{ \sqrt{1+ \frac{ \Delta R}{R} } }[/tex]

         

let's use a serial expansion

           √(1 ±x) = 1 ± ½ x +…

we substitute

         vₐ = v_ c ( [tex](1 + \frac{1}{2} \frac{\Delta M}{M} ) \ ( 1 - \frac{1}{2} \frac{\Delta R}{R} )[/tex])

we make the product and keep the terms linear

        vₐ = v_c  [tex]( \ 1 + \frac{1}{2} ( \frac{\Delta M}{M} - \frac{\Delta R}{R}) \ )[/tex]

The minimum escape speed, vc , for an object launched from the surface of the planet will be    [tex]v_a=v_c(1+\dfrac{1}{2}(\dfrac{\Delta M}{M}-\dfrac{\Delta R}{R})[/tex]

What is escape velocity of the planet?

The escape velocity is defined as the velocity required to send the object out of the gravitational influence of the earth.

To calculate the escape velocity let's use the conservation of energy

starting point. On the surface of the planet

    [tex]E_{mo} = K + U = \dfrac{1}{2} m v_c^2 - \dfrac{G Mm} { R}[/tex]

final point. At a very distant point

      [tex]E_{mf} = U = \dfrac{- G Mm }{ R_2}[/tex]

energy is conserved

         [tex]E{mo} = E{mf}[/tex]

          [tex]\dfrac{1}{2}m v_c^2 - \dfrac{G Mm} {R} = \dfrac{- G Mm }{ R_2}[/tex]

[tex]v_c^2 = 2 G M (\dfrac{1} {R} - \dfrac{ 1 }{R_2})[/tex]

if we consider the speed so that it reaches an infinite position R₂ = ∞

[tex]v_c = \sqrt{\dfrac{2GM}{R}[/tex]

         

now indicates that the mass and radius of the planet changes slightly

[tex]M ’= M + \Delta M = M(1+\dfrac{\Delta M}{M})[/tex]  

[tex]R ’= R + \Delta R = R (1+\dfrac{\Delta R}{R} )[/tex]

we substitute

   [tex]vₐ = \sqrt{\dfrac{2GM}{R} }\dfrac{\sqrt{1+\dfrac{\Delta M}{M}}} {\sqrt{1+\dfrac{\Delta R}{R}}}[/tex]

let's use a serial expansion

√(1 ±x) = 1 ± ½ x +…

we substitute

      [tex]v_a=v_c(1+\dfrac{1}{2}\dfrac{\Delta M}{M})(1-\dfrac{1}{2}\dfrac\Delta R}{R})[/tex]

Hence the minimum escape speed, vc , for an object launched from the surface of the planet will be    [tex]v_a=v_c(1+\dfrac{1}{2}(\dfrac{\Delta M}{M}-\dfrac{\Delta R}{R})[/tex]

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