A car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the frequency of the sound emitted by the horn? The speed of sound in air is 343 m/s
A) 68 Hz
B) 69 Hz
C) 70 Hz
D) 71 Hz
E) 72 Hz
C
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If a 20 W laser beam, which has an initial diameter of 2.0 mm, spreads out to a diameter of 2.0 m after traveling 10,000 m, what is the final intensity of the beam?
a. 
b. 
c. 
d. 
e. 
A sphere of pure U-235 will explode if it is
A) hot enough. B) shaken hard enough. C) big enough. D) none of the above
A 1.5-H inductor is connected in series with a 200-? resistor through a 15-V dc power supply and a switch. If the switch is closed at t = 0 s, what is the maximum energy stored by the inductor?
A) 1.2 mJ B) 2.2 mJ C) 3.2 mJ D) 4.2 mJ E) 5.2 mJ
Four equal +6.00-?C point charges are placed at the corners of a square 2.00 m on each side. (k = 1/4??0 = 8.99 × 109 N ? m2/C2)
(a) What is the electric potential (relative to infinity) due to these charges at the center of this square? (b) What is the magnitude of the electric field due to these charges at the center of the square?