Which of the following statements correctly explains why galaxy collisions should have been more common in the past than they are today?
A) Galaxies were closer together in the past, because the universe was smaller.
B) Galaxies were more active in the past and therefore would have collided with each other more frequently.
C) Galaxies were much bigger in the past, because they had not contracted completely.
D) Galaxies attracted each other more strongly in the past, because they had not yet turned most of their mass into stars.
A) Galaxies were closer together in the past, because the universe was smaller.
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A book is given a brief shove along a table top and released so that it slides a short distance and comes to rest. Galileo would say that the book stopped because
A) the ether slows it down to a stop. B) of friction. C) its natural motion is to come to rest. D) of its inertia. E) of gravity.
The increase of potential energy of the box is 100 J
Indicate whether the statement is true or false
A rocket can never go faster than the speed of its exhaust
Indicate whether the statement is true or false
A 10 solar mass star:
a) will eventually develop an Iron core b) can never produce a supernova c) will end its life as a white dwarf d) will live longer than the Sun on the Main Sequence e) can never become a neutron star