What observation has prompted astronomers to ponder the possible existence of dark energy?
a. discovery of quasars
b. discovery of superclusters
c. supernovae appear fainter than expected at large redshifts
d. uniform nature of the cosmic microwave background (CMB)
c
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A source emits sound at a fixed constant frequency f. If you run towards the source, the frequency you hear is
a. the same as f c. lower than f b. higher than f d. unrelated to f
A copper bar (d 5 10 mm, E 5 110 GPa) is loaded by tensile load P 5 11.5 kN. The maximum shear stress in the bar is approximately:
(A) 73 MPa
(B) 87 MPa
(C) 145 MPa
(D) 150 MPa
What are the circumstances under which convection can occur in a substance?
A) when the substance is subjected to a strong magnetic field B) when the substance is strongly cooled from underneath C) when dense material is being added to the substance D) when the substance is strongly shaken or disturbed by a strong wind E) when the substance is strongly heated from underneath
Two charges of 15 pC and ?40 pC are inside a cube with sides that are of 0.40-m length. Determine the net electric flux through the surface of the cube.
A. +2.8 N ? m2/C B. ?1.1 N ? m2/C C. +1.1 N ? m2/C D. ?2.8 N ? m2/C E. ?0.47 N ? m2/C