The ratio of kinetic energy of a planet at perigee and apogee during its motion around yhe sun in elliptical orbit of eccentricity is what?

You have forgotten to provide the value for eccentricity. But no worries, we can consider eccentricity to be a general term represented by e. Apogee is the point in the elliptical orbit where the planet is farthest from the sun and perigee is the point where the planet is nearest to sun.In order to calculate the ratio of kinetic energy, we can use conservation of angular momentum.
Now, we know that angular momentum is conserved for the planet throughout the orbit. Hence,
Angular momentum at apogee = angular momentum at perigee
Let ra be the distance at apogee and rp be the distance at perigee. The value of r1 and r2 can be represented in terms of the semi major axis and eccentricity (e) as mentioned below. If a is the length of semi major axis, then
ra= a(1+e)
and,
rp= a(1-e)
Now, by conservation of angular momentum, if the mass of the planet is m and the velocity at apogee and perigee be vand vp respectively.
m vra = m vp rp, or
va/vp = rp/ra = (1-e)/(1+e)
The ratio of kinetic energy is given by  = (1/2mvp2)/(1/2mva2) = (vp/va)2 =[(1+e)/(1-e)]2
 

  • 66
What are you looking for?