A 500-kg elevator is pulled upward by a cable that exerts a constant force of 5500 N on the elevator for a distance of 50.0 m. The elevator is the system
(a) What is the work done by the 5500-N force? (b) What is the work done by the gravitational force? (c) What is the net work done on the elevator?
(a) 275 Kj (b) -245 kJ (c) 30.0 kJ
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The maximum theoretical efficiency of a Carnot heat engine operating between reservoirs at the steam point and at room temperature is about:
A. 10% B. 20% C. 50% D. 80% E. 99%
Find the average density of a red giant star with a mass of 20 × 10^30 kg (approximately 10 solar masses) and a radius of 150 × 10^9 m (equal to the Earth's distance from the sun)
a. 1.41 × 10^-4 kg/m3 b. 0.007 kg/m3 c. 1.41 kg/m3 d. 710 kg/m3 e. 1.41 × 10^-3 kg/m3
Two uniform solid spheres have the same mass, but one has twice the radius of the other. The ratio of the larger sphere's moment of inertia to that of the smaller sphere is
A) 9/5. B) 8/5. C) 4/5. D) 4. E) 2.
Adding a few impurity atoms, like arsenic or gallium, to a semiconductor can produce
A. abundant thermal inversion. B. a significant increase in mass, even though the impurity atoms are quite sparse. C. gravitational repulsion of the impurity atoms, like the expanding universe. D. useful changes in the conductivity.