Photons of energy 4.20 eV bombard a surface, which emits photoelectrons with kinetic energies for 0 to 1.80 eV. What is the threshold frequency for this surface?
a. 
b. 
c. 
d. 
e. 
b.
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A typical "shooting star" during a meteor shower is caused by a ________ entering Earth's atmosphere.
A) boulder-size particle from an asteroid B) boulder-size particle from a comet C) pebble-size particle from an asteroid D) pebble-size particle from a comet E) microscopic particle of interstellar dust
Which living organisms most resemble the common ancestor of all life according to genetic testing?
A) bacteria such as E. coli B) organisms living deep in the oceans around seafloor volcanic vents and in hot springs C) plankton that use sunlight as an energy source through photosynthesis D) viruses E) stromatolites
Two point charges of values +2.0 and +5.5 ?C, respectively, are separated by 0.50 m. What is the potential energy of this 2-charge system? (ke = 8.99 × 10^9 N?m2/C2)
a. +0.50 J b. ?0.20 J c. +0.20 J d. ?0.41 J e. +0.41 J
A cylinder of weight W1 5 150 lb is supported at two points, 1 and 2, as shown. Neglect friction at the two points of contact. Normal forces N1 and N2 are (in lb):
(A) 75, 130
(B) 130, 75
(C) 125, 150
(D) 75, 120
