Briefly explain how dark matter affects the expansion rate of the universe and the significance of the term critical density in the absence of any mysterious repulsive force
What will be an ideal response?
Dark matter slows the expansion of the universe, because gravity is an attractive force. In the absence of any mysterious repulsive force (or dark energy), a universe with the average mass density equal to the critical density is the densest universe that will expand forever. A denser universe will eventually reverse its expansion and contract; a less dense universe will expand forever.
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Which of the following types of electromagnetic radiation has the highest frequency?
a. x-rays b. visible light c. radio d. gamma-rays e. infrared radiation
Forces and couples are applied to ABCDE as shown in the figure. All turns of ABCDE are 90o angles. The statically equivalent moment at A (MA) for the force2couple system is (in N?m)
(A) 2160i 1 575j 1 1480k
(B) 160i 1 425j 1 1380k
(C) 2160i 1 325j 1 1380k
(D) 2160i 1 325j 2 1480k
What is the number of moles of H2O produced if you combust 0.5 mole of CH4 according to the following balanced equation?
CH4 + 2 O2 ? CO2 + 2 H2O A) 2 moles B) 4 moles C) 6 moles D) 8 moles E) 1 mole
What accelerating potential in an electron microscope would give electrons a wavelength 10 m?
A. 37.5 V B. 75.0 V C. 150 V D. 300 V