Briefly discuss the rotation curve method, which is used for measuring the mass of a galaxy
What will be an ideal response?
The most precise method for measuring the mass of a galaxy is called the rotation curve method. It requires knowing the following: (1 ) the true sizes of the orbits of stars or gas clouds within a galaxy, which in turn requires knowing the distance of that galaxy; and (2 ) the orbital speeds of the stars or gas clouds, measured from the Doppler shifts of their spectral lines. That is enough information to use Kepler's third law and find the mass of the part of the galaxy contained within the star orbits with measured sizes and velocities. The rotation curve method works only for galaxies near enough to be well resolved. More distant galaxies appear so small that astronomers cannot measure the radial velocity at different points across the galaxy and must use other, less precise, methods to estimate masses.
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Some narrow rings of Saturn are seen in space probe photos to be caused by
a. gravitational interactions between ring particles. b. a spiral density wave which confines them. c. the magnetic field which holds them in place. d. small shepherd moons that orbit inside and outside the rings
Molecular Speeds: At what temperature would the root-mean-square speed of hydrogen, H2, molecules equal 11.2 km/s (the earth's escape speed)? The mass of a hydrogen atom is 1.67 × 10-27 kg, and the Boltzmann constant is 1.38 × 10-23 J/K.
A. 1.01 × 102 K B. 1.01 × 104 K C. 1.01 × 106 K D. 1.01 × 108 K
A constant horizontal pull acts on a sled on a horizontal frictionless ice pond. The sled starts from rest. When the pull acts over a distance x, the sled acquires a speed v and a kinetic energy K. If the same pull instead acts over twice this distance:
A) The sled's speed will be 2v and its kinetic energy will be 2K. B) The sled's speed will be 2v and its kinetic energy will be K . C) The sled's speed will be v and its kinetic energy will be 2K. D) The sled's speed will be v and its kinetic energy will be K . E) The sled's speed will be 4v and its kinetic energy will be 2K.
A metal rod of length L in a region of space where a constant magnetic field points into the page rotates clockwise about an axis through its center at constant angular velocity ?. While it rotates, the point(s) at lowest potential is(are)
A. A. B. B. C. C. D. D. E. A and E.