hi i hv these 2 doubts....i tried using the elliptic equation: r= a(1-e^2)/[1-e cos(theta)] however i cant really figure out how do i determine the answer,,i mean if i could know what exactly to do. 1) the orbit of venus is very near circular (e=0.0068).Assuming that the orbit is completely circular, what wud be the orbital motion of Venus if the mass of the sun were to suddenly drop by a factor of two?Would Venus be able to remain in the solar sysytem?if so at what radius cud it be found? 2)A satellite moves in an elliptic orbit with e= 0.5 around a planet from which it is launched.When it arrives at an apsis (a radial turning point),its velocity is suddenyl doubled .Show that the new orbit will be either paraboloc or hyperbolic according to which of the turning points the velocity doubling occurs? *** i really wanna know how to do these so that i can apply similar concepts to solve the other questions too.. also another quick question....given 'r' describing the motion of a planet in ,how can i find the speed? thanks.