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

Physics & Space Science

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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

Physics & Space Science

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.

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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

Physics & Space Science

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

Physics & Space Science