A box slides across a floor and comes to rest. The work done by the frictional force on the box is
a. positive
b. negative.
c. zero.
d. impossible to determine without knowing the coefficient of friction.
b
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Buoyancy: A 4.7-kg solid sphere, made of metal whose density is 4000 kg/m3, hangs by a light cord. When the sphere is immersed in water, what is the tension in the cord? The density of water is 1000 kg/m3.
A. 35 N B. 40 N C. 46 N D. 52 N E. 58 N
At atmospheric pressure, 45 moles of liquid helium are vaporized at its boiling point of 4.22 K. The heat of vaporization of helium, at atmospheric pressure, is 2.09 × 104 J/kg,
and the atomic weight of helium is 4.00 g/mol. The change in the entropy of the helium, as it vaporizes, is closest to A) 890 J/K. B) 14,000 J/K. C) 18,000 J/K. D) -9400 J/K. E) -14,000 J/K.
A projectile is launched from ground level at 15° above the horizontal and lands downrange. What other projection angle for the same speed would produce the same down-range distance?
A) 30° B) 45° C) 50° D) 75° E) 90°
Wave velocity is inversely proportional to
a. period. b. wavelength. c. amplitude. d. all of these.