The current definition of the standard second of time is based on
A) the frequency of radiation emitted by cesium atoms.
B) the earth's rotation rate.
C) the duration of one year.
D) the oscillation of a particular pendulum kept in France.
A
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Two parallel square metal plates that are 1.5 cm apart and 22 cm on each side carry equal but opposite charges uniformly spread out over their facing surfaces
How many excess electrons are on the negative surface if the electric field between the plates has a magnitude of 18,000 N/C? (k = 1/4??0 = 9.0 × 109 N ? m2/C2, e = 1.6 × 10-19 C)
Life forms in the Precambrian include
A) trilobites, brachiopods and stromatolites. B) cyanobacteria and trilobites. C) the agnatha and the coelacanths. D) stromatolites and certain primitive blue-green algae.
What is the mass of an object on which Earth exerts a gravitational force of 685 N near Earth's surface where g = 9.80 m/s2?
A) 69.9 kg B) 68.5 kg C) 71.3 kg D) 72.7 kg
A blimp is filled with 200 m3 of helium. How much mass can the balloon lift? The density of helium is one-seventh that of air, and the density of air is 1/800 that of water. Consider the mass of the balloon to be negligible
a. 115 kg b. 214 kg c. 315 kg d. 415 kg e. 37 kg