Why can't current theories describe what happened during the Planck era?
A) We do not yet have a theory that links quantum mechanics and general relativity.
B) We do not know how hot or dense the universe was during that time.
C) We do not understand the properties of antimatter.
D) The Planck era was the time before the Big Bang, and we cannot describe what happened before that instant.
A) We do not yet have a theory that links quantum mechanics and general relativity.
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Suppose a graph of distance traveled by a body versus time is constructed. The slope of the graph at any point may be identified with
A. instantaneous velocity. B. average speed. C. instantaneous acceleration. D. average acceleration.
A 1.8-kg block is released from rest at the top of a rough 30° inclined plane. As the block slides down the incline, its acceleration is 3.0 m/s2 down the incline. Determine the magnitude of the force of friction acting on the block
a. 4.2 N b. 3.0 N c. 3.4 N d. 3.8 N e. 2.3 N
A charge of +2 C is at the origin. When charge Q is placed at 2 m along the positive x axis, the electric field at 2 m along the negative x axis becomes zero. What is the value of Q?
a.
?3 C
b.
?6 C
c.
?7 C
d.
?8 C
Our universe will end in a big crunch
Indicate whether the statement is true or false