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physics
mechanics
Questions and Answers of
Mechanics
What is the dew point if the humidity is 65% on a day when the temperature is 25°C?
If the air pressure at a particular place in the mountains is 0.80 atm, estimate the temperature at which water boils.
What is the mass of water in a closed room 5.0 × 6.0 m × 2.4 m when the temperature is 25°C and the relative humidity is 55%?
A pressure cooker is a sealed pot designed to cook food with the steam produced by boiling water somewhat above 100°C. The pressure cooker in Fig. 13-32 uses a weight of mass m to allow steam to
Air that is at its dew point of 5°C is drawn into a building where it is heated to 22°C.What will be the relative humidity at this temperature? Assume constant pressure of 1.0 atm. Take into
When using a mercury barometer (Section 10-6), the vapor pressure of mercury is usually assumed to be zero. At room temperature mercury's vapor pressure is about 0.0015 mm-Hg. At sea level, the
Estimate the time needed for a glycine molecule (see Table 13-4) to diffuse a distance of 25μm in water at 20°C if its concentration varies over that distance from 1.00mol / m3 to 0.50 mol /
Oxygen diffuses from the surface of insects to the interior through tiny tubes called tracheae. An average trachea is about 2 mm long and has cross-sectional area of 2 × 10-9 m2. Assuming the
Determine the temperature at which the Celsius and Fahrenheit scales give the same numerical reading (TC = TF).
A precise steel tape measure has been calibrated at 14°C. At 37°C, (a) Will it read high or low? (b) What will be the percentage error?
A cubic box of volume 6.15 × 10-2 m3 is filled with air at atmospheric pressure at 15°C. The box is closed and heated to 165°C. What is the net force on each side of the box?
The gauge pressure in a helium gas cylinder is initially 32 atm. After many balloons have been blown up, the gauge pressure has decreased to 5 atm. What fraction of the original gas remains in the
If a scuba diver fills his lungs to full capacity of 5.5 L when 9.0 m below the surface, to what volume would his lungs expand if he quickly rose to the surface? Is this advisable?
A house has a volume of 1200 m3.(a) What is the total mass of air inside the house at 15°C?(b) If the temperature drops to - 15°C, what mass of air enters or leaves the house?
Estimate the number of air molecules in a room of length 6.0 m, width 3.0 m, and height 2.5 m. Assume the temperature is 22°C. How many moles does that correspond to?
A helium balloon, assumed to be a perfect sphere, has a radius of 24.0 cm. At room temperature (20°C), its internal pressure is 1.08 atm. Determine the number of moles of helium in the balloon, and
In an alcohol-in-glass thermometer, the alcohol column has length 12.61 cm at 0.0°C and length 22.79 cm at 100.0°C. What is the temperature if the column has length?(a) 18.70 cm,(b) 14.60 cm?
The density of gasoline at 0°C is 0.68 × 103 kg / m3.(a) What is the density on a hot day, when the temperature is 33°C?(b) What is the percent change in density?
If a steel band were to fit snugly around the Earth's equator at 25°C, but then was heated to 55°C, how high above the Earth would the band be (assume equal everywhere)?
(a) Estimate the rms speed of an amino acid, whose molecular mass is 89 u, in a living cell at 37°C.(b) What would be the rms speed of a protein of molecular mass 85,000 u at 37°C?
A 0.50-kg trash-can lid is suspended against gravity by tennis balls thrown vertically upward at it. How many tennis balls per second must rebound from the lid elastically, assuming they have a mass
In humid climates, people constantly dehumidify their cellars to prevent rot and mildew. If the cellar in a house (kept at 20°C) has 105 m2 of floor space and a ceiling height of 2.4 m, what is the
This Chapter gives two ways to calculate the thermal expansion of a gas at a constant pressure of 1.0 atm. Use both methods to calculate the volume change of 1000 L of an ideal gas as it goes from to
A scuba tank when fully charged has a pressure of 180 atm at 18°C. The volume of the tank is 11.3 L.(a) What would the volume of the air be at 1.00 atm and at the same temperature?(b) Before
A hot-air balloon achieves its buoyant lift by heating the air inside the balloon, which makes it less dense than the air outside. Suppose the volume of a balloon 1800 m3 is and the required lift is
Estimate how many molecules of air are in each 2.0-L breath you inhale that were also in the last breath Galileo took. Assume the atmosphere is about 10 km high and of constant density. What other
(a) The second postulate of kinetic theory is that the molecules are, on average, far apart from one another. That is, their average separation is much greater than the diameter of each molecule. Is
A paper cup placed among hot coals will burn if empty (note burn spots at top of cup in Fig. 14-14), but won't burn if filled with water. Explain. Forget the marshmallows.
On a cold windy day, a window will feel colder than on an equally cold day with no wind. This is true even if no air leaks in near the window. Why?
Will pasta cook faster if the water boils more vigorously? Explain.
1. When you put an ice cube in a glass of warm tea, which of the following happens?(a) Cold flows from the ice cube into the tea.(b) Cold flows from the ice cube into the tea and heat flows from the
1. It has been a hot summer, so when you arrive at a lake, you decide to go for a swim even though it is nighttime. The water is cold! The next day, you go swimming again during the hottest part of
For objects at thermal equilibrium, which of the following is true? (a) Each is at the same temperature. (b) Each has the same internal energy. (c) Each has the same heat. (d) All of the above. (e)
1. Which of the following happens when a material undergoes a phase change? (a) The temperature changes. (b) The chemical composition changes. (c) Heat flows into or out of the material. (d) The
1. A typical thermos bottle has a thin vacuum space between the shiny inner flask (which holds a liquid) and the shiny protective outer flask, often stainless steel. The vacuum space is excellent at
1. Radiation is emitted (a) Only by glowing objects such as the Sun. (b) Only by objects whose temperature is greater than the temperature of the surroundings. (c) Only by objects with more caloric
Ten grams of water is added to ten grams of ice in an insulated container. Will all of the ice melt? (a) Yes. (b) No. (c) More information is needed.
To what temperature will 8200 J of heat raise 3.0 kg of water that is initially at 10.0°C?
What is the specific heat of a metal substance if 135 kJ of heat is needed to raise 4.1 kg of the metal from 18.0°C to 37.2°C?
(a) How much energy is required to bring a 1.0-L pot of water at 20°C to 100°C? (b) For how long could this amount of energy run a 60-W lightbulb?
How long does it take a 750-W coffeepot to bring to a boil 0.75 L of water initially at 11°C? Assume that the part of the pot which is heated with the water is made of 280 g of aluminum, and that no
What will be the equilibrium temperature when a 265-g block of copper at 245°C is placed in a 145-g aluminum calorimeter cup containing 825 g of water at 12.0°C?
A 31.5-g glass thermometer reads 23.6°C before it is placed in 135 mL of water. When the water and thermometer come to equilibrium, the thermometer reads 41.8°C. What was the original temperature
A 0.40-kg iron horseshoe, just forged and very hot (Fig. 14-16), is dropped into 1.25 L of water in a 0.30-kg iron pot initially at 20.0°C. If the final equilibrium temperature is 25.0°C,
The heat capacity, C, of an object is defined as the amount of heat needed to raise its temperature by 1 C°. Thus, to raise the temperature by ∆T requires heat Q given byQ = C ∆T.(a) Write the
The 1.20-kg head of a hammer has a speed of 7.5 m/s just before it strikes a nail (Fig. 14-17) and is brought to rest. Estimate the temperature rise of a 14-g iron nail generated by eight such hammer
How much heat (in joules) is required to raise the temperature of 34.0 kg of water from 15°C to 95°C?
A 215-g sample of a substance is heated to 330°C and then plunged into a 105-g aluminum calorimeter cup containing 185 g of water and a 17-g glass thermometer at 10.5°C. The final temperature is
Determine the energy content of 100 g of Karen's fudge cookies from the following measurements. A 10-g sample of a cookie is allowed to dry before putting it in a bomb calorimeter. The aluminum bomb
If 3.40 × 105 J of energy is supplied to a container of liquid oxygen at -183° C how much oxygen can evaporate?
How much heat is needed to melt 23.50 kg of silver that is initially at 25°C?
During exercise, a person may give off 185 kcal of heat in 25 min by evaporation of water (at 20°C) from the skin. How much water has been lost?
What mass of steam at 100°C must be added to 1.00 kg of ice at 0°C to yield liquid water at 30°C?
A 28-g ice cube at its melting point is dropped into an insulated container of liquid nitrogen. How much nitrogen evaporates if it is at its boiling point of 77 K and has a latent heat of
High-altitude mountain climbers do not eat snow, but always melt it first with a stove. To see why, calculate the energy absorbed from your body if you: (a) Eat 1.0 kg of -15° C snow which your
When a diver jumps into the ocean, water leaks into the gap region between the diver's skin and her wetsuit, forming a water layer about 0.5 mm thick. Assuming the total surface area of the wetsuit
An iron boiler of mass 180 kg contains 730 kg of water at 18°C. A heater supplies energy at the rate of 58,000kJ/h. How long does it take for the water(a) To reach the boiling point,(b) To all have
Determine the latent heat of fusion of mercury using the following calorimeter data: 1.00 kg of solid Hg at its melting point of - 39° C is placed in a 0.620-kg aluminum calorimeter with 0.400 kg of
A cube of ice is taken from the freezer at - 8.5° C and placed in an 85-g aluminum calorimeter filled with 310 g of water at room temperature of 20.0°C. The final situation is all water at 17.0°C.
A 55-g bullet traveling at 250 m/s penetrates a block of ice at 0°C and comes to rest within the ice. Assuming that the temperature of the bullet doesn't change appreciably, how much ice is melted
One end of a 56-cm-long copper rod with a diameter of 2.0 cm is kept at 460°C, and the other is immersed in water at 22°C. Calculate the heat conduction rate along the rod.
(a) How much power is radiated by a tungsten sphere (emissivity ε = 0.35) of radius 19 cm at a temperature of 25°C?(b) If the sphere is enclosed in a room whose walls are kept at - 5° C, what is
How long does it take the Sun to melt a block of ice at 0°C with a flat horizontal area 1.0 m2 and thickness 1.0 cm? Assume that the Sun's rays make an angle of 35° with the vertical and that the
Suppose 150 W of heat flows by conduction from the blood capillaries beneath the skin to the body's surface area of 1.5 m2. If the temperature difference is 0.50 C°, estimate the average distance of
Two rooms, each a cube 4.0 m per side, share a 14-cmthick brick wall. Because of a number of 100-W lightbulbs in one room, the air is at 30°C, while in the other room it is at 10°C. How many of the
A 100-W lightbulb generates 95 W of heat, which is dissipated through a glass bulb that has a radius of 3.0 cm and is 0.50 mm thick. What is the difference in temperature between the inner and outer
Approximately how long should it take 8.2 kg of ice at 0°C to melt when it is placed in a carefully sealed Styrofoam ice chest of dimensions 25 cm × 35 cm, × 55 cm whose walls are 1.5 cm thick?
A copper rod and an aluminum rod of the same length and cross-sectional area are attached end to end (Fig. 14-18). The copper end is placed in a furnace maintained at a constant temperature of
Suppose the insulating qualities of the wall of a house come mainly from a 4.0-in. layer of brick and an R-19 layer of insulation, as shown in Fig. 14-19.What is the total rate of heat loss through
(a) Estimate the total power radiated into space by the Sun, assuming it to be a perfect emitter at T = 5500 K. The Sun’s radius is 7.0 × 108 m. (b) From this, determine the power per unit
A British thermal unit (Btu) is a unit of heat in the British system of units. One Btu is defined as the heat needed to raise 1 lb of water by 1 F°. Show that 1 Btu = 0.252 kcal = 1056 J.
A mountain climber wears a goose-down jacket 3.5 cm thick with total surface area 0.95 m2. The temperature at the surface of the clothing is and at the skin is 34°C. Determine the rate of heat flow
During light activity, a 70-kg person may generate 200 kcal/h. Assuming that 20% of this goes into useful work and the other 80% is converted to heat, estimate the temperature rise of the body after
A bicyclist consumes 9.0 L of water over the span of 3.5 hours during a race. Making the approximation that 80% of the cyclist's energy goes into evaporating this water (at 20°C) as sweat, how much
A 310-kg marble boulder rolls off the top of a cliff and falls a vertical height of 120 m before striking the ground. Estimate the temperature rise of the rock if 50% of the heat generated remains in
A 2.3-kg lead ball is placed in a 2.5-L insulated pail of water initially at 20.0°C. If the final temperature of the water-lead combination is 32.0°C, what was the initial temperature of the lead
A microwave oven is used to heat 250 g of water. On its maximum setting, the oven can raise the temperature of the liquid water from 20°C to 100°C in 1 min 45 s (= 105 s). (a) At what rate does the
How many joules and kilocalories are generated when the brakes are used to bring a 1300-kg car to rest from a speed of 95 km/h?
The temperature within the Earth's crust increases about 1.0 C° for each 30 m of depth. The thermal conductivity of the crust is 0.80 J/s ∙ C° ∙ m.(a) Determine the heat transferred from the
An iron meteorite melts when it enters the Earth's atmosphere. If its initial temperature was - 105° C outside of Earth's atmosphere, calculate the minimum velocity the meteorite must have had
The temperature of the glass surface of a 75-W lightbulb is 75°C when the room temperature is 18°C. Estimate the temperature of a 150-W lightbulb with a glass bulb the same size. Consider only
In a cold environment, a person can lose heat by conduction and radiation at a rate of about 200W. Estimate how long it would take for the body temperature to drop from 36.6°C to 35.6°C if
After a hot shower and dishwashing, there seems to be no hot water left in the 65-gal (245-L) water heater. This suggests that the tank has emptied and refilled with water at roughly 10°C. (a) How
A house thermostat is normally set to 22°C, but at night it is turned down to 16°C for 9.0 h. Estimate how much more heat would be needed (state as a percentage of daily usage) if the thermostat
An automobile cooling system holds 18 L of water. How much heat does it absorb if its temperature rises from 15°C to 95°C?
Create graphs similar to Fig. 14-5, but for lead and ethyl alcohol. Compare and contrast them with each other and with the graph for water. Are there any temperature ranges for which all three
(a) Using the solar constant, estimate the rate at which the whole Earth receives energy from the Sun.(b) Assume the Earth radiates an equal amount back into space (that is, the Earth is in
A house has well-insulated walls 19.5 cm thick (assume conductivity of air) and area 410 m2, a roof of wood 5.5 cm thick and area 250 m2, and uncovered windows 0.65 cm thick and total area 33 m2.(a)
The COPs are defined differently for heat pumps and air conditioners. Explain why.
Can the temperature of a system remain constant even though heat flows into or out of it? If so, give examples.
What are the high-temperature and the low-temperature areas for? (a) An internal combustion engine, (b) A steam engine? Are they, strictly speaking, heat reservoirs?
1. In an isobaric compression of an ideal gas, (a) No heat flows into the gas. (b) The internal energy of the gas remains constant. (c) No work is done on the gas. (d) Work is done on the gas. (e)
1. About what percentage of the heat produced by burning gasoline is turned into useful work by a typical automobile? (a) 20%. (b) 50%. (c) 80%. (d) 90%. (e) Nearly 100%. 2. Which statement is
An ideal gas undergoes an isobaric compression and then an isovolumetric process that brings it back to its initial temperature. Had the gas undergone one isothermal process instead, (a) The work
1. An ideal gas undergoes an isothermal expansion from state A to state B. In this process (a) Q = 0, ∆U = 0, W > 0. (b) Q > 0, ∆U = 0, W < 0. (c) Q = 0, ∆U > 0, W > 0. (d) Q > 0, ∆U = 0, W
1. An ideal gas undergoes an adiabatic expansion, a process in which no heat flows into or out of the gas. As a result, (a) The temperature of the gas remains constant and the pressure decreases. (b)
1. On a very hot day, could you cool your kitchen by leaving the refrigerator door open?(a) Yes, but it would be very expensive.(b) Yes, but only if the humidity is below 50%.(c) No, the refrigerator
An ideal gas expands isothermally, performing 4.30 × 103 J of work in the process. Calculate (a) The change in internal energy of the gas, (b) The heat absorbed during this expansion.
Consider the following two-step process. Heat is allowed to flow out of an ideal gas at constant volume so that its pressure drops from 2.2 atm to 1.4 atm. Then the gas expands at constant pressure,
The PV diagram in Fig. 15-23 shows two possible states of a system containing 1.75 moles of a monatomic ideal gas. (P1 = P2 = 425 N / m2, V1 = 2.00 m3, V2 = 8.00 m3.)(a) Draw the process which
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