One kilogram of chilled water (0°C) is placed in a freezer which is kept at 0°F (?18°C). Approximately how much electric energy (in kilocalories) is needed just to freeze the water if the room temperature is maintained at 75°F (24°C)? (LF,ice = 333 J/g; cice = 2.09 J/g?°C.)
A. 11
B. 15
C. 16
D. 13
E. 33
Answer: D
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A jar holds 2.0 L of ideal nitrogen gas, N2, at STP. The atomic mass of nitrogen is 14.0 g/mol, the ideal gas constant is R = 8.31 J/mol ? K, Avogadro's number is NA = 6.022 × 1023 molecules/mol, and 1.00 atm = 101 kPa
(a) How many moles of nitrogen are in the jar? (b) How many nitrogen molecules are in the jar? (c) What is the mass of the nitrogen in the jar?
Faraday's Law: A flat square coil of wire with 15 turns and an area of 0.40 m2 is placed with the plane of its area parallel to a magnetic field of 0.75 T. The coil is flipped so its plane is perpendicular to the magnetic field in a time of 0.050 s. What is the magnitude of the average induced emf in the coil?
A. 6.0 V B. 36 V C. 45 V D. 90 V
When we say that a cluster of galaxies is acting as a gravitational lens, what do we mean?
A) It magnifies the effects of gravity that we see in the cluster. B) It is an unusually large cluster that has a lot of gravity. C) It bends or distorts the light coming from galaxies located behind it. D) The overall shape of the cluster is that of a lens.
A 1.15-kg grinding wheel 22.0 cm in diameter is spinning counterclockwise at a rate of 20.0 revolutions per second. When the power to the grinder is turned off,
the grinding wheel slows with constant angular acceleration and takes 80.0 s to come to a rest. (a) What was the angular acceleration (in rad/s2 ) of the grinding wheel as it came to rest if we take a counterclockwise rotation as positive? (b) How many revolutions did the wheel make during the time it was coming to rest?