If the intensity of an electromagnetic wave is 80 MW/m2, what is the amplitude of the magnetic field of this wave? (c = 3.0 × 108 m/s, ?0 = 4? × 10-7 T • m/A, ?0 = 8.85 × 10-12 C2/N • m2)
A) 0.82 mT
B) 0.33 µT
C) 10 T
D) 14 T
E) 0.58 mT
A
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Impulse: The graph in the figure shows the x component F of the net force that acts for 10 s on a 100-kg crate. What is the change in the momentum of the crate during the 10 s that this force acts?
A. -100 kg ? m/s B. -25 kg ? m/s C. 75 kg ? m/s D. -75 kg ? m/s E. 25 kg ? m/s
When charging two objects by rubbing them together
a. Neither may be a conductor. b. They must be made of different material. c. They will sometimes end up with both being positively charged. d. The heat produced by friction is a necessary part of this process.
To change the fundamental frequency of a guitar string, you can
A. strum it over the sound hole. B. do nothing short of using a completely different guitar. C. use something other than a pick. D. make it shorter, by pressing a finger of your left hand on the string.
The horizontal component of the buttressing force at the base of a pointed arch is
A) less than that of a rounded arch. B) equal to that of a rounded arch. C) greater than that of a rounded arch. D) zero in magnitude.