Two planets travel in circular orbits about a star. The period of planet A is T, while that of planet B is 3T. What is the ratio of their orbital radii, R_A/R_B?

A. 0.69

B. 0.48

C. 0.19

D. 0.33

When the escape speed from the surface of a spherical object of mass M and radius R is equal to the speed of light, that radius is called the Schwarzschild radius for the given mass. What is the Schwarzschild radius of the Sun, whose mass is 2.0 10³⁰ kg? (i.e., if all the Sun's mass were compressed into a sphere of this radius, the escape speed from its surface would be the speed of lightit would become a black hole!)

A. 3.0 km

B. 5.9 km

C. 1.5 km

D. 4.5 km