Molecular Speeds: Dust particles in a grain elevator frequently have masses of the order of 1.0 × 10-9 kg. If, to a first approximation, we model the dust particles as an ideal gas, what would be the rms speed of such a particle in air at 27°C? The Boltzmann constant is 1.38 × 10-23 J/K.
A. 3.5 × 10-6 m/s
B. 5.6 × 10-5 m/s
C. 7.8 × 10-4 m/s
D. 5.2 × 10-3 m/s
E. 4.9 × 10-2 m/s
Answer: A
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Consider the space time diagram below, which shows events A and B and the world lines of clocks that one might use to measure the time between those events.
The clock(s) following which world line(s) measure(s)
(a) the space time interval between events A and B?
(b) a proper time between events A and B?
(c) a coordinate time between events A and B?
(d) the shortest time interval between events A and B?
(e) the longest time interval between events A and B?
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Suppose that there are 10 billion (10,000,000,000,000 ) habitable planets in our galaxy, that 1 in 5 habitable planets has life, that 1 in 1000 planets with life has at some point had an intelligent civilization, and that 1 in 1000 civilizations that
have ever existed is in existence now. How many civilizations would exist at present? A) 200,000 B) 2,000,000 C) 20,000 D) 20,000,000
Not only does the central engine of active galaxies and quasars require a black hole, but also ________ to provide the radiative energy
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