Astronomers infer that the universe is expanding because distant galaxies all appear to
A) be growing in size.
B) be moving away from us, with more distant ones moving faster.
C) be made mostly of dark matter.
D) rotate rapidly.
B
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In stellar astronomy, _____ states that the weight of each layer of a star must be supported by the layer below
A) the law of conservation of mass B) the law of conservation of energy C) the law of hydrostatic equilibrium D) the law of energy transport
A hot-wire anemometer is used to determine the boundary layer velocity profile in the air flow over a scale model of an automobile. The hot-wire is held in a traversing mechanism that moves the wire in a direction normal to the surface of the model. The hot-wire is operated at constant temperature. The boundary layer thickness is to be defined as the distance from the model surface at which the velocity is 90% of the free stream velocity. If the probe current is I0, when the hot-wire is held in the free stream velocity, U?, what current indicates the edge of the boundary layer? Neglect radiation heat transfer from the hot-wire and conduction from the ends of the wire.
GIVEN • Thin, electrically-heated constant-temperature wire in air flow near an automobile model • Boundary layer thickness ° point when velocity (Uy) = 90% free stream velocity Vo • Probe current at U? = Io FIND • Probe current at edge of the boundary layer (Ib) ASSUMPTIONS • Radiation is negligible • Conduction from the ends of the hot-wire is negligible • Reynolds number is small
A magnesium alloy that has the designation “AZ31” has _________ percent aluminum.
Fill in the blank(s) with the appropriate word(s).
Although the Sun's core has a density much greater than rock, it is considered a gaseous object because
A. the Sun formed from the Solar nebula which itself was a large gas and dust cloud. B. the Sun's high internal temperature prevent the atoms from bonding together to form a liquid or a solid. C. it is composed mostly of hydrogen. D. a large fraction of the Sun's interior is made of electromagnetic radiation (light).