Visible, luminous matter (such as the stars within galaxies) amounts to what percentage of the critical density (the density of mass-energy needed to make the geometry of the universe flat)?
A) 25 percent B) 50 percent C) less than 1 percent D) 10 percent
C
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What will be an ideal response?
The horizontal and vertical components of the initial velocity of a football are 16 m/s and 20 m/s respectively. How long does it take for the football to rise to the highest point of its trajectory?
A) 1.0 s B) 2.0 s C) 3.0 s D) 4.0 s E) 5.0 s
A long thin rod of length L has a linear density ?(x) = A(L-x)2 where x is the distance from the left end of the rod. (a) How far is the center of mass of the rod from the left end of the rod? (b) What is the mass of the rod?
What will be an ideal response?
It is decided to electropolish a complex cast copper sculpture, because the surface is too complex for mechanical polishing, and the as-cast surface does not have the required appearance. Through experimentation with piece of copper, it is found that a current density of 1 A/cm2 produces the required appearance. It is estimated that the entire surface of the sculpture is 100 cm2 , and it is decided to electropolish the sculpture at 100 A of current. No more than 0.0001 m of copper should be removed from the sculpture, so that the design shape is not altered. Determine the maximum time for electropolishing if the process is 100 % efficient?
What will be an ideal response?