A helicopter stays aloft by pushing large quantities of air downward every second. What mass of air must be pushed downward at 30.0 m/s every second to keep a 1000 kg helicopter aloft?
a. 120 kg
c. 327 kg
b. 245 kg
d. 490 kg
C
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A useful method of expressing very small or very large numbers is
A) scientific notation. B) arabic numerals. C) roman numerals. D) significant figures. E) greek letters.
Current: A total of 2.0 × 1013 electrons pass a given point in a wire in 15 s. What is the current in the wire? (e = 1.60 × 10-19 C)
A. 1.3 mA B. 1.3 A C. 0.21 ?A D. 3.2 ?A
An earthquake S wave travels through
a. the inner core only. b. the mantle only. c. the outer core only. d. all of these.
The habitable zone is
a. the region on a planet where conditions are acceptable for life to exist. b. a region around a star where a planet's temperature would permit the existence of liquid water. c. very small for a massive star. d. only found around G and K stars. e. a region on a young planet where amino acids can begin to form DNA molecules.