| № |
Condition |
free/or 0.5$ |
| 55763 | Explain why a column of mercury in a thermometer first descends slightly and then rises when the thermometer is placed into hot water? |
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| 55764 | Every second at Niagara Falls (Fig P22.52), some 5 000 m3 of water falls a distance of 50.0 m. What is the increase in entropy per second due to the falling water? Assume that the mass of the surroundings is so great that its temperature and that of the water stay nearly constant at 20.0°C. Suppose that a negligible amount of water evaporates. |
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| 55765 | Every morning at seven o’clock there’s twenty terriers drilling on the rock. The boss comes around and he says, “Keep still and bear down heavy on the cast-iron drill and drill, ye terriers, drill.” And drills, ye terriers, drill its work all day for sugar in your tea down beyond the railway. And drill, ye terriers, drill .The foreman’s name was John McAnn. By God, he was a blamed mean man. One day a premature blast went off And a mile in the air went big Jim Goff. And drill ... Then when next payday came around Jim Goff a dollar short was found. When he asked what for, came this reply: “You were docked for the time you were up in the sky.” And drill... —American folksong What was Goff’s hourly wage? State the assumptions you make in computing it. |
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| 55766 | Ethyl alcohol has about half the specific heat of water. If equal-mass samples of alcohol and water in separate beakers are supplied with the same amount of energy, compare the temperature increases of the two liquids |
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| 55767 | Estimate the mass of the air in your bedroom. State the quantities you take as data and the value you measure or estimate for each. |
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| 55768 | “Energy is the mistress of the Universe and entropy is her shadow.” Writing for an audience of general readers, argue for this statement with examples. Alternatively, argue for the view that entropy is like a decisive hands-on executive instantly determining what will happen, while energy is like a wretched back-office bookkeeper telling us how little we can afford. |
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| 55769 | Emily challenges her friend David to catch a dollar bill as follows. She holds the bill vertically, as in Figure P2.44, with the center of the bill “between David” is index finger and thumb. David must catch the bill after Emily releases it without moving his hand downward. If his reaction time is 0.2 s, will he succeed? Explain your reasoning. |
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| 55770 | An electron in a cathode ray tube (CRT) accelerates from 2.00 x 104 m/s to 6.00 x 106 m/s over 1.50 cm.
(a) How long does the electron take to travel this 1.50 cm?
(b) What is its acceleration? |
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| 55771 | An electric power plant that would make use of the temperature gradient in the ocean has been proposed. The system is to operate between 20.0°C (surface water temperature) and 5.00°C (water temperature at a depth of about 1 km).
(a) What is the maximum efficiency of such a system?
(b) If the useful power output of the plant is 75.0 MW, how much energy is taken in from the warm reservoir per hour?
(c) In view of your answer to part (a), do you think such a system is worthwhile? Note that the “fuel” is free. |
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| 55772 | An electric power plant has an overall efficiency of 15.0%. The plant is to deliver 150 MW of power to a city, and its turbines use coal as the fuel. The burning coal produces steam that drives the turbines. This steam is then condensed to water at 25.0°C by passing it through cooling coils in contact with river water.
(a) How many metric tons of coal does the plant consume each day (1 metric ton = 103 kg)?
(b) What is the total cost of the fuel per year if the delivered price is $8.00/metric ton?
(c) If the river water is delivered at 20.0°C, at what minimum rate must it flow over the cooling coils in order that its temperature not exceed 25.0°C? (Note: The heat of combustion of coal is 33.0 kJ/g) |
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| 55773 | Each year thousands of children are badly burned by hot tap water. Figure P19.12 shows a cross-sectional view of an anti scalding faucet attachment designed to prevent such accidents. Within the device, a spring made of material with a high coefficient of thermal expansion controls a movable plunger. When the water temperature rises above a preset safe value, the expansion of the spring causes the plunger to shut off the water flow. If the initial length L of the unstressed spring is 2.40 cm and its coefficient of linear expansion is 22.0 X 10-6 (°C)-1, determine the increase in length of the spring when the water temperature rises by 30.0°C. (You will find the increase in length to be small. For this reason actual devices have a more complicated mechanical design, to provide a greater variation in valve opening for the temperature change anticipated.) |
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| 55774 | During the power stroke in a four-stroke automobile engine, the piston is forced down as the mixture of combustion products and air undergoes an adiabatic expansion (Fig. P21.32). Assume that (1) the engine is running at 2 500 cycles/min, (2) the gauge pressure right before the expansion is 20.0 atm, (3) the volumes of the mixture right before and after the expansion are 50.0 and 400 cm3, respectively, (4) the time involved in the expansion is one-fourth that of the total cycle, and (5) the mixture behaves like an ideal gas with specific heat ratio 1.40. Find the average power generated during the expansion. |
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| 55775 | During the compression stroke of a certain gasoline engine, the pressure increases from 1.00 atm to 20.0 atm. If the process is adiabatic and the fuel–air mixture behaves as a diatomic ideal gas, (a) by what factor does the volume change and (b) by what factor does the temperature change? (c) Assuming that the compression starts with 0.016 0 mol of gas at 27.0°C, find the values of Q, W, and ΔEint that characterize the process. |
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| 55776 | During periods of high activity, the Sun has more sunspots than usual. Sunspots are cooler than the rest of the luminous layer of the Sun’s atmosphere (the photosphere).
Paradoxically, the total power output of the active Sun is not lower than average but is the same or slightly higher than average. Work out the details of the following crude model of this phenomenon. Consider a patch of the photosphere with an area of 5.10 % 1014 m2. Its emissivity is 0.965.
(a) Find the power it radiates if its temperature is uniformly 5 800 K, corresponding to the quiet Sun.
(b) To represent a sunspot, assume that 10.0% of the area is at 4 800 K and the other 90.0% is at 5 890 K. That is, a section with the surface area of the Earth is 1 000 K cooler than before and a section nine times as large is 90 K warmer. Find the average temperature of the patch.
(c) Find the power output of the patch. Compare it with the answer to part (a). (The next sunspot maximum is expected around the year 2012.) |
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| 55777 | During operation the breaker hammer develops on the concrete surface a force which is indicated in the graph. To achieve this the 2-lb spike S is fired from rest into the surface at 200 ft/s. Determine the speed of the spike just alter rebounding. |
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| 55778 | Draw motion diagrams for
(a) An object moving to the right at constant speed,
(b) An object moving to the right and speeding up at a constant rate,
(c) An object moving to the right and slowing down at a constant rate,
(d) An object moving to the left and speeding up at a constant rate, and
(e) An object moving to the left and slowing down at a constant rate. (f) How would your drawings change if the changes in speed were not uniform; that is, if the speed were not changing at a constant rate? |
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| 55779 | A dog’s hair has been cut and is now getting 1.04 mm longer each day. With winter coming on, this rate of hair growth is steadily increasing, by 0.132 mm/day every week. By how much will the dog’s hair grow during 5 weeks? |
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| 55780 | Does the second law of thermodynamics contradict or correct the first law? Argue for your answer. |
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| 55781 | A diving bell in the shape of a cylinder with a height of 2.50 m is closed at the upper end and opens at the lower end. The bell is lowered from air into sea water (p =| 1.025 g/cm3). The air in the bell is initially at 20.0°C. The bell is lowered to a depth (measured to the bottom of the bell) of 45.0 fathoms or 82.3 m. At this depth the water temperature is 4.0°C, and the bell is in thermal equilibrium with the water. (a) How high does sea water rise in the bell? (b) To what minimum pressure must the air in the bell be raised to expel the water that entered? |
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| 55782 | Discuss three common examples of natural processes that involve an increase in entropy. Be sure to account for all parts of each system under consideration. |
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