A star enters the main sequence when ________.
A. it forms planets
B. nuclear fuel in its core can supply enough energy to stop its collapse
C. it collapses, and its envelope becomes degenerate
D. it stops fusing nuclear fuel in its core and starts to expand
Answer: B
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The purity of an alloy is given by the _____________.
Fill in the blank(s) with the appropriate word(s).
If the force on a body is halved then the acceleration of the body
a. increases by half b. increases by double c. decreases by half d. decreases by double
An 80-km/h airplane caught in a 60-km/h crosswind has a resultant speed of
A) 60 km/h. B) 80 km/h. C) 100 km/h. D) 141 km/h.
Ultraviolet light is shone on a piece of metal that has a known work function, and electrons are observed being produced through the interaction of the light with the metal. The lamp that produces the light is now replaced with a lamp of the same intensity, but which produces photons having a longer wavelength. What difference is observed in the number of electrons produced per unit time?
A. The same number are produced. B. More are produced. C. Without knowing more about the wavelengths used, one cannot answer. D. Fewer are produced.