A car starts from point A, goes 100 km to point B, immediately turns around, and returns to point A. The round trip takes 4 hours. What is the average speed of the car?

The sun’s mass is 2.0×10^ 30 kg, its radius is 7.0×10 5 km, and it has a rotational period of approximately 28 days. if the sun should collapse into a white dwarf of radius 3.5×10 3 km, what would its period be if no mass were ejected and a sphere of uniform density can model the sun both before and after?