How do we account for the great variety of substances in the world?
A) The Earth is 4.5 billion years old.
B) Most of these substances are organic compounds.
C) Atoms are incredibly small.
D) There are many possible combinations of atoms.
Ans: D) There are many possible combinations of atoms.
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During the Carboniferous Period,
A) the carbon dioxide cycle started to operate for the first time B) carbon-rich meteorites impacted the Earth C) the first carbon-based life appeared D) land was covered with dense forests with the appearance of the first insects and amphibians
Two identical silver spheres of mass m and radius r are placed a distance R (sphere 1) and 2R (sphere 2) from the sun respectively. The ratio of the gravitational force exerted by the sun on sphere 1 to the pressure of solar radiation on sphere 1 is T1; the ratio for sphere 2 is T2 . The ratio of T2 to T1 is
a. 0.25. b. 0.50. c. 1.0. d. 2.0. e. 4.0.
A radioactive sample is to be stored in a protective box with 4-cm-thick walls having interior dimensions 4 cm* 4 cm* 12 cm. The radiation emitted by the sample is completely absorbed at the inner surface of the box, which is made of concrete. If the outside temperature of the box is 25°C, but the inside temperature is not to exceed 50°C, determine the maximum permissible radiation rate from the sample, in watts.
GIVEN
A radioactive sample in a protective concrete box
Wall thickness (t) = 4 cm = 0.4 m
Box interior dimensions: 4 x 4 x 12 cm
All radiation emitted is completely absorbed at the inner surface of the box
The outside temperature of the box (To) = 25°C
The maximum inside temperature (Ti) = 50°C
FIND
The maximum permissible radiation rate from the sample, q (in watts)
ASSUMPTIONS
The system is in steady state
SKETCH
Blue stars are hotter than red stars
a. True b. False Indicate whether the statement is true or false