How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
A) by matter that has been converted to pure energy by interacting with the jets shot out by a central black hole
B) by nuclear fusion near a central black hole
C) by matter-antimatter annihilation near a central black hole
D) by magnetic fields that trap and accelerate charged particles, which then radiate large amounts of energy
E) by gravity, which converts the potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter
E
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A bit of matter that enters Earth's atmosphere and survives to reach the ground is called
a. a meteor. b. a meteoroid. c. a meteorite. d. a minor planet. e. an asteroid.
Figure 4–53 shows a block (mass mA) on a smooth horizontal surface, connected by a thin cord that passes over a pulley to a second block which hangs vertically.
(a) Draw a free-body diagram for each block, showing the force of gravity on each, the force (tension) exerted by the cord, and any normal force.
(b) Apply Newton’s second law to find formulas for the acceleration of the system and for the tension in the cord. Ignore friction and the masses of the pulley and cord.
The requirement of liquid water is the most severe constraint on the development of life
Indicate whether the statement is true or false
Four traveling waves are described by the following equations, where all quantities are measured in SI units and y represents the displacement
I: y = 0.12 cos(3x + 2t) II: y = 0.15 sin(6x - 3t) III: y = 0.23 cos(3x + 6t) IV: y = -0.29 sin(1.5x - t) Which of these waves have the same speed? A) I and III B) I and IV C) II and III D) I and II E) III and IV