Which observation(s) support(s) the idea that dark energy accounts for about 70% of the total mass-energy density of the universe?
A) This is just the right amount of a repulsive force to explain the observed acceleration in the expansion of the universe.
B) This is just the right amount of energy, in addition to the observed matter and dark matter, to explain the pattern of temperatures in the cosmic microwave background.
C) It is the right amount of energy to make the universe geometrically flat, which is mathematically easier to work with than a curved geometry.
D) A and B
E) B and C
D
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What kinematic quantity is indicated by the speedometer of an automobile?
Inside an accelerating spaceship far from gravitational influences, a flashlight beam will
A) not bend. B) curve as it would in a gravitational field equal to the acceleration of the spaceship. C) follow a semi-circular path.
The "seeing" ability or resolution of radiation is determined by its wavelength. If the size of an atom is approximately 1.3 × 10^?10 m, how fast must an electron travel to have a wavelength smaller than that of an atom? (me = 9.11 × 10^?31 kg and h = 6.63 × 10^?34 J?s)
a. 5.6E+6 m/s b. 5.1E+7 m/s c. 8.4E+5 m/s d. 9.5E+6 m/s e. 2.4E+3 m/s
Mercury is heated from 100ºF to vapor at 800ºF. Assume hnfg is 122 Btu/lbm at 676ºF and use a cP of 0.032 Btu/lbm ·ºF for liquid mercury and 0.015 for the vapor. Determine the enthalpy change per unit mass and the heat per unit mass.
What will be an ideal response?