A policeman in a stationary car measures the speed of approaching cars by means of an ultrasonic device that emits a sound with a frequency of 39.6 kHz
A car is approaching him at a speed of 35.0 m/s. The wave is reflected by the car and interferes with the emitted sound producing beats. What is the frequency of the beats when the speed of sound in air is 343 m/s?
A) 5000 Hz
B) 4500 Hz
C) 8490 Hz
D) 9000 Hz
E) 4250 Hz
D
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Molecular Speeds: At what temperature would the root-mean-square speed of hydrogen, H2, molecules equal 11.2 km/s (the earth's escape speed)? The mass of a hydrogen atom is 1.67 × 10-27 kg, and the Boltzmann constant is 1.38 × 10-23 J/K.
A. 1.01 × 102 K B. 1.01 × 104 K C. 1.01 × 106 K D. 1.01 × 108 K
________ is the study of the universe, including its properties, structure, and evolution
Fill in the blank(s) with the appropriate word(s)
The first quarter moon will rise about noon, and set about midnight
Indicate whether the statement is true or false
What is the angular resolution of the eye at a wavelength of 500 nm for a pupil diameter of 2.8 mm?
A. 
B. 
C. 
D. 
E. 