What do we mean when we say the universe becomes transparent at 400,000 years after the Big Bang?
A) the universe ends at that time
B) Helium nuclei formed then and since they are transparent it was possible to see to larger distances
C) we can only see from one end of the universe to another if we existed before that time
D) electromagnetic radiation (light) can travel freely through the universe so we can see to large distances
E) protons and neutrons formed then and since they are transparent it was possible to see to larger distances
Ans: D) electromagnetic radiation (light) can travel freely through the universe so we can see to large distances
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Newton never knew the numerical value of "his" universal gravitational constant G
Indicate whether the statement is true or false
Multiple-Object Accelerating Systems: Two boxes P and Q on a perfectly smooth horizontal surface are connected by a light horizontal cord. The mass of P is greater than that of Q. A horizontal force 
is applied to box Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P is
A. zero. B. less than F but not zero. C. equal to F. D. greater than F.
The resistance of an object is defined as
A) (length)/(resistivity)(cross-sectional area). B) (current)/(voltage). C) (voltage)/(current). D) (length)(resistivity)(cross-sectional area). E) (voltage)(current).
Inside a house, stepping on a tile floor barefooted may feel almost cold, but stepping on carpet in an adjacent room feels comfortably warm. Why is this?
a. It's because the tile is below room temperature while the carpet is at room temperature. b. It's because the tile is at room temperature while carpet is normally warmer. c. It's because the thermal conductivity of tile is less than that of carpet. d. It's because the thermal conductivity of carpet is less than that of tile.