To find the distance of nearby stars, we use their parallaxes obtained over ________-month intervals
A) one B) three C) six D) twelve E) twenty-four
C
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Suppose you repeated the famous COBE and Planck observations of the cosmic microwave background, with a slight different observational setup, to check their results. Which of the following observations would be surprising and contradict earlier findings?
A) You find that cosmic microwave background has a temperature of 2.73 K. B) You find that cosmic microwave background has an almost perfect thermal spectrum. C) You find that cosmic microwave background contains redshifted emission lines of hydrogen and helium. D) You find that cosmic microwave background looks essentially the same in all directions. E) You find that cosmic microwave background has tiny temperature fluctuations at the level of about 1 part in 100,000.
A uniform rod is 2.0 m long. The rod is pivoted about a horizontal, frictionless pin through one end. The rod is released from rest at an angle of 30° above the horizontal. What is the angular acceleration of the rod at the instant it is released?
a. 4.7 rad/s2 b. 6.9 rad/s2 c. 6.4 rad/s2 d. 5.6 rad/s2 e. 4.2 rad/s2
A book of mass m is projected with a speed v across a horizontal surface. The book slides until it stops due to the friction force between the book and the surface. The surface is now tilted 30°, and the book is projected up the surface with the same initial speed v. When the book has come to rest, how does the decrease in mechanical energy of the book-Earth system compare to that when the book
slid over the horizontal surface? 1.It's the same. 2.It’s larger on the tilted surface. 3.It’s smaller on the tilted surface. 4.More information is needed.
Percent of Freshwater
What will be an ideal response?