What is the essential reason that all perpetual motion machines fail?
a. Perpetual motion machines must create energy in order to do useful work, and energy cannot be created.
b. Perpetual motion machines must at least preserve all the energy in a system, and some is always lost.
c. Perpetual motion machines run on gasoline, and gasoline is not a renewable resource.
d. A perpetual motion machine necessarily removes heat from a single-temperature environment.
e. Perpetual motion machines have to contend with friction, which destroys energy.
b
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An automobile initially moving 72. km/hr jams the brakes and skids to a stop in a distance of 24. meters on a dry pavement but stops in 81.6 m for a wet pavement (the auto weighs 2211. lbs, neglect reaction delay)
(a) What is the coefficient of friction for dry weather? (b) What is the coefficient in wet weather conditions? (c) Is this the STATIC or the KINETIC coefficient?
The speed of the electron in the Bohr theory of hydrogen is
a. proportional to n. b. proportional to n2. c. inversely proportional to n. d. inversely proportional to n2.
Which planet is orbited by the four "Galilean moons" known individually as Io, Europa, Ganymede, and Callisto?
A) Saturn B) Uranus C) Mars D) Jupiter E) Neptune
The Chandra X-Ray Observatory must operate in space because
A) X-rays are too dangerous to be allowed on the ground. B) X-rays do not penetrate Earth's atmosphere. C) X-ray telescopes require the use of grazing incidence mirrors. D) It was built by NASA.