For electric power that costs 10 cents per kilowatt hour, the cost of operating a 110-V heater that uses 20 A for 10 hours is
A) $0.22.
B) $0.55.
C) $2.20.
D) $5.50.
E) none of the above
Answer: C
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Suppose that an object doubles its luminosity in 10 hours. What can we conclude?
A) The object must be a quasar. B) The object must be a Cepheid variable star. C) The object is no more than about 10 light-hours across. D) The object must be very far away, making it one of the most luminous objects in the universe. E) The object is being orbited by another object with an orbital period of 10 hours.
Current understanding holds that a galaxy's type (spiral, elliptical, or irregular)
A) is always determined by the angular momentum of the protogalactic cloud that formed it. B) may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies. C) is determined by whether the galaxy is located in a cluster where collisions are likely or outside a cluster where collisions are less likely. D) may either be a result of the mass of the protogalactic cloud that formed it or the result of the heavy element abundance in that cloud.
When water of mass m and specific heat c is heated at constant pressure from absolute temperature T1 to absolute temperature T2, its change in entropy is what?
a. cm ln(T2/T1) b. cm (T2/T1) c. cm (T2 ? T1)/T1 d. cm (T2 ? T1)/T2 e. cm (T2 ? T1)/(T2 + T1)
A thin copper rod 1.0 m long has a mass of 0.050 kg and is in a magnetic field of 0.10 T. What minimum current in the rod is needed in order for the magnetic force to cancel the weight of the rod?
A) 1.2 A B) 2.5 A C) 4.9 A D) 7.6 A E) 9.8 A