What originally caused the sun to heat up?
A) The gases from which it formed had already been heated by the Big Bang.
B) A nearby supernova explosion that occurred during the early stages of the formation of the sun.
C) Nuclear fusion reactions that occurred during the time when the sun's gases were spread out and beginning to fall together by gravitational attraction.
D) As the sun's gases gathered together by their own gravity, they accelerated inward and collided.
E) Electromagnetic radiation from outside the sun heated the sun's gases as they gathered together.
D
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An aluminum cantilever beam (E 5 72 GPa) with a square cross section and span length L 5 2.5 m is sub- jected to uniform load q 5 1.5 kN/m. The allowable bending stress is 55 MPa. The maximum deflection of the beam is approximately:
(A) 10 mm
(B) 20 mm
(C) 30 mm
(D) 40 mm
Why do scientists assume that the early universe was much hotter and denser than the universe of today?
A) The fact that the universe is expanding implies that objects were closer together in the past, and compressing material makes it hotter and denser. B) All objects begin their existence in a hot and dense state. C) The fact that the universe is filled with stars and galaxies implies that matter must once have been hot to have made these objects. D) Observations of distant galaxies show that they are much hotter than galaxies of today, suggesting that the whole universe was hotter in the past.
A long wire carrying a 2.0-A current is placed along the y-axis. What is the magnitude of the magnetic field at a point 0.60 m along the x-axis?
A) 6.7 × 10-7 T B) 13 × 10-7 T C) 1.2 × 10-7 T D) 6.7 T E) 12 T
A force of 30N stretches a very light ideal spring 0.73m from equilibrium. What is the force constant (spring constant) of the spring?
A) 34 N/m B) 41 N/m C) 46 N/m D) 22 N/m