The Sun rotates now with a rotation speed of about 2 km/sec. If its radius shrank to the size of Earth, about how fast would it spin?
A) 20 km/sec.
B) 2,000 km/sec.
C) 200 km/sec.
D) 0.2 km/sec.
E) 400 km/sec.

Question

Quizplus · Accepted Answer

The Sun's angular momentum would be conserved as it shrinks. Since angular momentum L = Iω (moment of inertia times angular velocity), and I is proportional to the square of the radius, if the radius decreases, the angular velocity must increase to keep L constant. The radius of the Sun is about 109 times that of Earth, so the rotation speed would increase by a factor of about 109, leading to approximately 200 km/sec.

The Sun Rotates Now with a Rotation Speed of About