Consider a point on a bicycle tire that is momentarily in contact with the ground as the bicycle rolls across the ground with constant speed. The direction for the acceleration for this point at that moment is:
a. upward.
b. down toward the ground.
c. forward.
d. at that moment the acceleration is zero.
a
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Text boxes, check boxes, and option buttons are all elements of what type of web tool?
A. forms B. comments fields C. databases D. login pages
One reason the planets near the Sun are composed mainly of rock and iron may be that
A. the Sun is made mostly of iron, so the planets nearest it are formed of iron. B. the Sun's heat made it difficult for ices and gases to condense near it. C. the Sun's gravity sucked in iron and heavy material and the lighter materials floated farther away. D. the Sun's magnetic field attracted all the iron into the region around the Sun.
What prevents a brown dwarf from undergoing nuclear fusion?
A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. B) There is not enough mass to maintain nuclear reactions in a self-sustaining way. C) The surface temperature never rises high enough for the radiation to be trapped and heat its interior to the temperature required for nuclear fusion. D) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. E) There are too many heavy elements and not enough hydrogen for fusion to occur in a self sustaining way.
Of the Galilean satellites, which has the oldest, most heavily cratered surface?
A) Titan B) Io C) Europa D) Callisto E) Ganymede