Which has a greater mass? A) four protons B) two neutrons and ...

[nummyann]

Which has a greater mass?
 
  A) four protons
  B) two neutrons and two protons in a helium nucleus
  C) A and B both have exactly the same mass.

Question 2

Briefly describe two different ways of measuring the mass of a cluster of galaxies.
 
  What will be an ideal response?

[morganmarie791]

Answer to Question 1

A

Answer to Question 2

There are three basic methods: The first method is to apply a form of the orbital velocity law to a group of galaxies. The second method relies on measuring the temperature of hot X-ray gas in the intracluster medium. Because the intracluster medium is nearly in a state of gravitational equilibrium, the average kinetic energies of the gas particles (which we find by measuring the temperature of the gas) are determined primarily by the strength of gravity and hence by the amount of mass within the cluster. The third method uses gravitational lensing to determine the mass of the cluster. The light-bending angle of a gravitational lens depends on the mass of the cluster, so we can measure the mass by observing how strongly the cluster distorts light paths of more distant galaxies. All three methods generally agree with one another.

[nummyann]

Excellent

[kthug]

Gracias!