1. The problem statement, all variables and given/known data Comet moves around the sun in a very ellipical orbit around the sun. As it approach, in 1986, Comet Halley was 8.79x10^7km from the sun and moving with a speed of 54.6km/s. What will be the comet's speed be when it crosses Neptune's orbit in 2006? length of comet from the sun = 8.79x10^7km = 8.79x10^10 m v of comet = 54.6km/s = 54.6x10^3m/s T = 20 years length of neptune from the sun = 4.50x10^12m 2. Relevant equations i use the equation T^2 = (4*pie*r^3)/GM and K2 + U2 = K1 + U1 3. The attempt at a solution i first use the Kelper's rule to find M of the comet, but i don't really know if that's the right step to start with. Thank you.