Most meteoroids--rocks moving through outer space--have been moving for billions of years. What, if anything, keeps them moving and why?
A) According to Newton's law of motion, their own acceleration keeps them moving.
B) According to the law of inertia, nothing is needed to keep them moving.
C) According to current theories about the creation of the universe, the big bang keeps them moving.
D) According to Newton's law of gravity, the force of gravity keeps them moving.
E) According to Newton's law of gravity, nothing is needed to keep them moving.
B
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The energy generated by the Sun is released by the _______ to make _______ nuclei
a. fusion of H nuclei; He b. fusion of He nuclei; H c. fission of H nuclei; He d. fission of He nuclei; H
List guidelines for selecting images. Describe methods for ensuring your web images are usable and accessible. ?
What will be an ideal response?
How do we determine the amount of dark matter in elliptical galaxies?
A) We measure the broadening of the galaxy's absorption lines to infer the speeds of stars at different distances from the galactic center. B) We measure how fast the galaxy rotates as a whole. C) We measure the orbital velocities of star-forming gas clouds in the outer portion of the galaxy. D) We count the number of stars in the galaxy. Combining this with the galaxy's volume, we can calculate the galaxy's density. E) We search for dark lanes of dust and black holes within the galaxy.
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
