If you measure the velocity of a cloud of gas that is rotating around the center of a galaxy in a circular orbit with radius R, you can determine:
A) the total mass of the galaxy
B) the mass of the stars and gas in the galaxy
C) the mass of the galaxy enclosed within the radius R
D) the mass of the galaxy located outside the radius R
E) the mass of luminous matter within the radius R

Question

Quizplus · Accepted Answer

By using Kepler's laws of motion and assuming that the gas cloud is in a circular orbit, we can determine the mass of the galaxy enclosed within the radius R. This is known as the "virial theorem" and can be used to estimate the mass of galaxies and other astronomical objects. The other choices are not necessarily true based solely on measurements of the gas cloud's velocity.

If You Measure the Velocity of a Cloud of Gas