Prior to 1991, most astronomers assumed that gamma-ray bursts came from neutron stars (with accretion disks) within the Milky Way Galaxy. How do we now know that this hypothesis was wrong?
A) Observations from the Compton Gamma-Ray Observatory showed that gamma-ray bursts occur too frequently to be attributed to neutron stars.
B) Observations from the Compton Gamma-Ray Observatory showed that gamma-ray bursts come randomly from all directions in the sky.
C) Observations from the Compton Gamma-Ray Observatory allowed us to trace gamma-ray bursts to pulsating variable stars in distant galaxies.
D) We now know that gamma-ray bursts come not from neutron stars but from black holes.
E) Theoretical work has proven that gamma rays cannot be produced in accretion disks.
B
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A simply supported beam (L 5 4.5 m) with rectangular cross section (b 5 95 mm, h 5 280 mm) supports uniform load q 5 25 kN/m. The ratio of the magnitudes of the principal stresses (?1/?2) at a point a 5 1.0 m from the left support and distance d 5 100 mm up from the bottom of the beam is approximately:
(A) 9
(B) 17
(C) 31
(D) 41
Which jovian planets in our solar system have rings?
A) Saturn only B) Jupiter and Saturn only C) all but Neptune D) all four of the jovian planets have rings.
A stepped steel shaft with diameters d1 5 56 mm and d2 5 52 mm is twisted by torques T1 5 3.5 kN # m and T2 5 1.5 kN # m acting in opposite directions. The maximum shear stress is approximately:
(A) 54 MPa
(B) 58 MPa
(C) 62 MPa
(D) 79 MPa
A string with a fixed frequency vibrator at one end is subjected to varying tensions. When the tension is 20 N, a resonance with 3 antinodes results. What tension would cause a resonance with 2 antinodes in this string?
a. 30 N b. 45 N c. 80 N d. 8.9 N e. 13 N