2a: A extrasolar system of planets consists of a star (mass 5.1 x10³⁰ kg) and two planets. The first planet has a mass of 5.7 x 10²⁴ kg and the second planet has a mass of 8.1 x 10²³ kg. At one point in time the system is arranged in a straight line that has the two planets located at the ends of the line. The distance from the star to the first planet is 5.9 x 10¹⁰ m and the distance from the star to the second planet is 4.6 x 10¹² m. What is the gravitational potential energy of the system when it is in this alignment?

2b: Two ropes are attached to a circular disk that has a radius of 29.5 m. The ropes are pulled such that they are tangent to the disk. One force is 4.7 N and would cause a clockwise rotation of the disk if it were the only force on the disk. The other force is 30.0 N and would cause a counterclockwise rotation. What is the net torque on the disk? (clockwise torque is negative)