## Reduction to One Body Problem

Let be the mass of the satellite, be the mass of Jupiter, be the vector from the satellite to the planet, and be the angle between the satellite and Jupiter where We will proceed to use polar coordinates in our calculations. The kinetic energy and potential energy of the system are and respectively. Therefore, the Lagrangian is . Applying the Euler-Lagrange equation to the coordinate, we have

Applying the Euler-Lagrange equation on the coordinate, we have

From equation , we have that . Note that since angular momentum is conserved in this system, . Substituting this into equation , we get . Integrating with respect to time, we have

which is a statement of conservation of energy. Solving in terms of , we have

Note that this is equivalent to

Rewriting the conservation of angular momentum, we have Substituting this into equation , we have

Integrating both sides, we have

where is the initial angle. Evaluating this integral, we have

We can rewrite this as

Recognizing this as the general equation of a conic, we know that the eccentricity of the orbit is determined by

## Solution of 2001 AP ® PHYSICS C: MECHANICS FREE-RESPONSE QUESTION Mech 2. Part C

(i) If the speed of the satellite is slightly faster, note that the eccentricity will be , implying an elliptical orbit. Additionally, note that . If the satellite is slightly faster, will increase and thus will increase except for when , where , that is, when the satellite passes the injection point.

(ii) If the speed of the satellite is slightly slower, note that the eccentricity will be , implying an elliptical orbit. Additionally, note that . If the satellite is slightly slower, will decrease and thus will decrease except for when , where , that is, when the satellite passes the injection point.