From the 1970s to the present, the accepted value of H has almost doubled, so:
A) the age of the universe is twice as old as we originally believed.
B) the age of the Universe is half what we believed.
C) the Copernican principle is not valid beyond our solar system.
D) the ages of the oldest globular clusters are invalid.
E) the critical density must also be halved.
B
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A compact disk rotates at 210 revolutions per minute. What is its angular speed in rad/s?
A) 11.0 rad/s B) 22.0 rad/s C) 45.3 rad/s D) 69.1 rad/s E) 660 rad/s
Liquid oxygen (LOX) for the Space Shuttle can be stored at 90 K prior to launch in a spherical container 4 m in diameter. To reduce the loss of oxygen, the sphere is insulated with superinsulation developed at the U.S. Institute of Standards and Technology’s Cryogenic Division that has an effective thermal conductivity of 0.00012 W/(m K). If the outside temperature is 20°C on the average and the LOX has a heat of vaporization of 213 J/g, calculate the thickness of insulation required to keep the LOX evaporation rate below 200 g/h.
GIVEN
FIND
- The minimum thickness of the insulation (L) to keep evaporation rate below 0.2 kg/h
ASSUMPTIONS
- The thickness is small compared to the sphere diameter so the problem can be considered one
dimensional
- Steady state conditions prevail
- Radiative heat loss is negligible
SKETCH
If the magnitude difference between one star and another is 1, the stars differ in brightness by a factor of
a. 10. b. 100. c. 2.51. d. 4.
The dimensional equivalence of the quantity "momentum" in terms of the fundamental quantities (mass, length, time) is:
a. MLT?1. b. ML2T?2. c. MLT. d. MLT?2.