Suppose you read somewhere that 10 percent of the matter in the Milky Way is in the form of dust grains. Should you be surprised? If so, why?
A) Given how easily dust grains can form, 10 percent is a surprisingly low fraction.
B) The fraction of 10 percent is surprisingly high because dust grains can form only at low temperatures.
C) There is nothing surprising about the 10 percent figure because dust grains are the material from which stars are born.
D) The fraction of 10 percent cannot be correct. Dust grains are solid and only 2 percent of the matter in the galaxy is made of anything besides hydrogen and helium.
D
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The threshold of hearing is
a. 0 dB. b. 140 dB. c. 40 dB. d. 110 dB. e. 1 dB.
A charged particle (m = 5.0 g, q = ?70 ?C) moves horizontally at a constant speed of 30 km/s in a region where the free fall gravitational acceleration is 9.8 m/s2 downward, the electric field is 700 N/C upward, and the magnetic field is perpendicular to the velocity of the particle. What is the magnitude of the magnetic field in this region?
a. 47 mT b. zero c. 23 mT d. 35 mT e. 12 mT
What two observations allow us to calculate the Galaxy's mass?
A) the Sun's mass and velocity in orbit of the Galactic Center B) the Sun's age and period of the Galactic Year C) the Sun's orbital velocity and its distance from the Galactic Center D) the Sun's mass and its age E) the Sun's composition and luminosity
An unfueled 1000-kg experimental rocket sled at rest on level frictionless rails is loaded with 50 kg of propellant. It exhausts the propellant in a 20 s "burn.". The rocket moves at 160 m/s after the burn. What average force is experienced by the rocket during the burn?
a. 0.80 × 10^4 N b. 0.75 × 10^4 N c. 0.60 × 10^4 N d. 0.35 × 10^4 N