A coal-fired plant generates 600 MW of electric power. The plant uses 4.8 × 106 kg of coal each day. The heat of combustion of coal is 3.3 × 107 J/kg
The steam that drives the turbines is at a temperature of 300°C, and the exhaust water is at 37°C. (a) What is the overall efficiency of the plant for generating electric power? (b) What is the Carnot efficiency? (c) How much thermal energy is exhausted each day?
(a) 33%
(b) 46%
(c) 1.1 × 1014 J
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Which of the following things is an “extended object”? For each item, answer “A” if the item is an acceptable extended object, “B” if the definition of an extended object applies badly to the item, and “D” if it is debatable.
(a) An electron (b) An atom (c) A rock (d) A swarm of bees (e) The earth’s atmosphere (f) The water in an ocean current (g) Sugar molecules dissolved in a cup of water (h) The vacuum between galaxies
The SI base units for the spring constant are which of the following?
a. kg•s2 c. kg/s2 b. kg/m2 d. kg•m2
When the reflection of an object is seen in a concave mirror the image will
a. always be real. b. always be virtual. c. may be either real or virtual. d. will always be enlarged.
A spaceship moves at a speed of 0.95c away from the Earth. It shoots a star wars torpedo toward the Earth at a speed of 0.90c relative to the ship. What is the velocity of the torpedo relative to the Earth? (The direction in which the spaceship moves is the positive direction.)
a. ?0.34c b. 0.34c c. 0.060c d. ?0.060c e. 0