# Equilibrium physics help!

• Nov 27th 2009, 07:45 AM
jddery
Equilibrium physics help!
The Cassini probe, mass 5,712 kg, is in a circular orbit with a radius of 1.2×108 m around the planet Saturn. How much work must its engine do to change it to a circular orbit with a radius of 1.1×109 m?
[Mass of Saturn = 5.68×1026 kg]

• Nov 27th 2009, 08:20 AM
Quote:

Originally Posted by jddery
The Cassini probe, mass 5,712 kg, is in a circular orbit with a radius of 1.2×108 m around the planet Saturn. How much work must its engine do to change it to a circular orbit with a radius of 1.1×109 m?
[Mass of Saturn = 5.68×1026 kg]

HI

According to the energy principles ,

Word done = the change in total energy of the satellite , U

$\triangle U=U_f-U_i$

$=-\frac{GMm}{2r'}-(-\frac{GMm}{2r})$

$=\frac{GMm}{2}[\frac{1}{r}-\frac{1}{r'}]$

$
=\frac{6.67\times 10^{-11}\times 5.68\times 1026\times 5712}{2}[\frac{1}{1.2\times 108}-\frac{1}{1.1\times 109}]
$

$
=-9.26\times 10^{-6}J
$
• Nov 27th 2009, 04:19 PM
jddery
how are you getting G?
how are you getting G