Questions and Answers of Inquiry into Physics

The lightbulb used in a computer projector has a resistance of 80 V. What is the current through the bulb when it is operating on 120 V?
Combine Ohm’s law and the equation for power consumption to derive the equation that gives the power in terms of current and resistance. Use the result to answer the following question. A cable
Imagine a company offering a line of hair dryers that operate on different voltages, say, 12, 30, 60, and 120 V. Assume that all of the dryers are rated at 1,200 W and find the current that would
Compute the number of electrons that flow through a wire each second when the current in the wire is 0.2 A.
Compute the electric force acting between the electron and the proton in a hydrogen atom. The radius of the smallest orbit of the electron around the proton is about 5.3 3 10-11 m.
What are the frequencies of the first four harmonics of middle C (261.6 Hz)?
The sound level measured in a room by a person watching a movie on a home theater system varies from 65 dB during a quiet part to 95 dB during a loud part. Approximately how many times louder is the
A person stands at a point 300 m in front of the face of a sheer cliff. If the person shouts, how much time will elapse before an echo is heard?
A baseball fan sitting in the ?cheap seats? is 150 m from home plate . How much time elapses between the instant the fan sees a batter hit the ball and the moment the fan hears the sound? 150 m
A sonic depth gauge is placed 5 m above the ground. An ultrasound pulse sent downward reflects off snow and reaches the device 0.03 seconds after it was emitted. The air temperature is -20oC.(a) How
A person riding on a bus hears the sound from a horn on a car that is stopped. What is different about the sound when the bus is approaching the car compared to when the bus is moving away from the
A person stands directly in front of two speakers that are emitting the same pure tone. The person then moves to one side until no sound is heard. At that point, the person is 7 m from one of the
In a student laboratory exercise, the wavelength of a 40,000-Hz ultrasound wave is measured to be 0.868 cm. Find the air temperature.
The frequency of middle C on the piano is 261.6 Hz.(a) What is the wavelength of sound with this frequency as it travels in air at room temperature?(b) What is the wavelength of sound with this
A wave traveling 80 m/s has a wavelength of 3.2 m. What is the frequency of the wave?
A 4-Hz continuous wave travels on a Slinky. If the wavelength is 0.5 m, what is the speed of waves on the Slinky?
What is the speed of sound in air at the normal boiling temperature of water?
Two children stretch a jump rope between them and send wave pulses back and forth on it. The rope is 3 m long, its mass is 0.5 kg, and the force exerted on it by the children is 40 N.(a) What is the
An irreversible process takes place by which the entropy of the universe increases by 1.67 J/K. If the temperature of the environment in which the process occurred is 220 K, how much energy was made
As a gasoline engine is running, an amount of gasoline containing 15,000 J of chemical potential energy is burned in 1 s. During that second, the engine does 3,000 J of work.(a) What is the
What is the Carnot efficiency of a heat engine operating between the temperatures of 300oC (573 K) and 100oC (373 K)?
The temperature of the air in thermals decreases about 10oC for each 1,000 m they rise. If a thermal leaves the ground with a temperature of 30oC and a relative humidity of 31 percent, at what
An apartment has the dimensions 10 m by 5 m by 3 m. The temperature is 25oC, and the relative humidity is 60 percent. What is the total mass of water vapor in the air in the apartment?
Inside a building, the temperature is 20oC, and the relative humidity is 40 percent. How much water vapor is there in each cubic meter of air?
On a winter day, the air temperature is 215oC, and the humidity is 0.001 kg/m3.(a) What is the relative humidity?(b) When this air is brought inside a building, it is heated to 20oC. If the humidity
A 10-kg lead brick is dropped from the top of a 629-m-tall television transmitting tower in North Dakota and falls to the ground. Assuming all of its energy goes to heat it, what is its temperature
A 1,200-kg car going 25 m/s is brought to a stop using its brakes. Let’s assume that a total of approximately 20 kg of iron in the brakes and wheels absorbs the heat produced by the friction.(a)
(a) Compute the amount of heat needed to raise the temperature of 1 kg of water from its freezing point to its normal boiling point.(b) How does your answer to (a) compare to the amount of heat
How much heat is needed to raise the temperature of 5 kg of silver from 208C to 960°C?
A fixed amount of a particular ideal gas at 16oC and a pressure of 1.75 x 105 Pa occupies a volume of 2.75 m3. If the volume is increased to 4.20 m3 and the temperature is raised to 26.4oC, what will
A machinist wishes to insert a steel rod with a diameter of 5 mm into a hole with a diameter of 4.997 mm. By how much would the machinist have to lower the temperature of the rod to make it fit the
An iron railroad rail is 700 ft long when the temperature is 30oC. What is its length when the temperature is 210oC?
What are the three common temperature scales? What are the normal boiling and freezing points of water in each scale?
Air flows through a heating duct with a square crosssection with 8-inch sides at a speed of 5.0 ft/s. Just before reaching an outlet in the floor of a room, the duct widens to assume a square
The wing of an airplane has an average cross-sectional area of 12 m2 and experiences a lift force of 75,000 N. What is the average difference in the air pressure between the top and bottom of the
A dentist’s chair with a person in it weighs 1900 N. The output plunger of a hydraulic system starts to lift the chair when the dental assistant’s foot exerts a force of 45 N on the input piston.
A scale reads 100 N when a piece of aluminum is hanging from it. What does it read when it is lowered so that the aluminum is submerged in water?
The volume of an iceberg is 100,000 ft3 (Figure 4.57).(a) What is its weight, assuming it is pure ice?(b) What is the volume of seawater it displaces when floating? (You know what the weight of the
A box-shaped piece of concrete measures 3 ft by 2 ft by 0.5 ft.(a) What is its weight?(b) Find the buoyant force that acts on it when it is submerged in water.(c) What is the net force on the
A blimp used for aerial camera views of sporting events holds 200,000 ft3 of helium.(a) How much does the helium weigh?(b) What is the buoyant force on the blimp at sea level?(c) How much can the
An ebony log with volume 12 ft3 is submerged in water. What is the buoyant force on it?
Calculate the gauge pressure at a depth of 300 m in seawater.
Find the gauge pressure at the bottom of a swimming pool that is 12 ft deep.
The volume of the Drop Tower “Bremen” (a 100-meter-tall tube used to study processes during free fall) is 1,700 m3.(a) What is the mass of the air that must be removed from it to reduce the
A large balloon used to sample the upper atmosphere is filled with 900 m3 of helium. What is the mass of the helium?
A large tanker truck can carry 20 tons (40,000 lb) of liquid.(a) What volume of water can it carry?(b) What volume of gasoline can it carry?
A large chunk of metal has a mass of 393 kg, and its volume is measured to be 0.05 m3.(a) Find the metal’s mass density and weight density in SI units.(b) What kind of metal is it?
A box-shaped metal can has dimensions 8 in. by 4 in. by 10 in. high. All of the air inside the can is removed with a vacuum pump. Assuming normal atmospheric pressure outside the can, find the total
A large truck tire is inflated to a gauge pressure of 80 psi. The total area of one sidewall of the tire is 1,200 in.2. What is the outward force on the sidewall because of the air pressure?
A grain silo is filled with 2 million pounds of wheat. The area of the silo’s floor is 400 ft2. Find the pressure on the floor in pounds per square foot and in psi.
Two small 0.25-kg masses are attached to opposite ends of a very lightweight rigid rod 0.5 m long. The system is spinning in a horizontal plane around a vertical axis perpendicular to the rod located
In the annual Empire State Building race, contestants run up 1,575 steps to a height of 1,050 ft. In 2003, Australian Paul Crake completed the race in a record time of 9 min and 33 s. Mr. Crake
A particular hydraulic pile driver uses a ram with a mass of 1040 kg. If the maximum pile energy is 11,780 J, how high must the ram be raised to achieve this value? Assuming it takes 0.62 s for the
How long does it take a worker producing 200 W of power to do 10,000 J of work?
The ceiling of an arena is 20 m above the floor. What is the minimum speed that a thrown ball would need to just reach the ceiling?
A bicycle and rider going 10 m/s approach a hill. Their total mass is 80 kg.(a) What is their kinetic energy?(b) If the rider coasts up the hill without pedaling, how high above its starting level
At NASA’s Zero Gravity Research Facility in Cleveland, Ohio, experimental payloads fall freely from rest in an evacuated vertical shaft through a distance of 132 m.(a) If a particular payload has a
A 25-kg child uses a pogo stick to bounce up and down. The spring constant, k, of the toy equals 8750 N/m. (a) By how much would the spring be compressed by the child if she simply balanced
An archer using a simple bow exerts a force of 180 N to draw back the bow string 0.50 m.(a) What is the average work done by the archer in preparing to launch her arrow? (Compute the average work as
In compressing the spring in a toy dart gun, 0.5 J of work is done. When the gun is fired, the spring gives its potential energy to a dart with a mass of 0.02 kg.(a) What is the dart’s kinetic
The kinetic energy of a motorcycle and rider is 60,000 J. If their total mass is 300 kg, what is their speed?
A motorist runs out of gas on a level road 200 m from a gas station. The driver pushes the 1,200-kg car to the gas station. If a 150-N force is required to keep the car moving, how much work does the
A loaded gun is dropped on a frozen lake. The gun fires, with the bullet going horizontally in one direction and the gun sliding on the ice in the other direction. The bullet’s mass is 0.02 kg, and
A 50-kg boy on roller skates moves with a speed of 5 m/s. He runs into a 40-kg girl on skates. Assuming they cling together after the collision, what is their speed?
A pitcher throws a 0.5-kg ball of clay at a 6-kg block of wood. The clay sticks to the wood on impact, and their joint velocity afterward is 3 m/s. What was the original speed of the clay?
A sprinter with a mass of 65 kg reaches a speed of 10 m/s during a race. Find the sprinter’s linear momentum.
As a spacecraft approaches a planet, the rocket engines on it are fired (turned on) to slow it down so it will go into orbit around the planet. The spacecraft’s mass is 2,000 kg, and the thrust
On a highway curve with radius 50 m, the maximum force of static friction (centripetal force) that can act on a 1,000-kg car going around the curve is 8,000 N. What speed limit should be posted for
A hang glider and its pilot have a total mass equal to 120 kg.While executing a 3608 turn, the glider moves in a circle with an 8-m radius. The glider’s speed is 10 m/s.(a) What is the net force on
Under certain conditions, the human body can safely withstand an acceleration of 10 g.(a) What net force would have to act on someone with mass of 50 kg to cause this acceleration?(b) Find the weight
At the end of an amusement park ride, it is desirable to bring a gondola to a stop without having the acceleration exceed 2 g. If the total mass of the gondola and its occupants is 2,000 kg, what is
As a baseball is being caught, its speed goes from 30 to 0 m/s in about 0.005 s. Its mass is 0.145 kg.(a) What is the baseball’s acceleration in m/s2 and in g’s? (b) What is the size of the
A person stands on a scale inside an elevator at rest (Figure 2.54). The scale reads 800 N.(a) What is the person?s mass?(b) The elevator accelerates upward momentarily at the rate of 2 m/s2. What
The engines in a supertanker carrying crude oil produce a net force of 20,000,000 N on the ship. If the resulting acceleration is 0.1 m/s2, what is the ship’s mass?
As a 2-kg ball rolls down a ramp, the net force on it is 10 N. What is the acceleration?
The mass of a subway car and passengers is 40,000 kg. If its acceleration as it leaves a station is 0.9 m/s2, what is the net force acting on it?
Suppose an airline allows a maximum of 30 kg for each suitcase a passenger brings along.(a) What is the weight in newtons of a 30-kg suitcase?(b) What is the weight in pounds?
The graph in Figure 1.40 shows the velocity versus time for a bullet as it is fired from a gun, travels a short distance, and enters a block of wood. Compute the acceleration at the times marked a,
The roller coaster in Figure 1.39 starts at the top of a straight track that is inclined 30? with the horizontal. This causes it to accelerate at a rate of 4.9 m/s2 (1/2 g).(a) What is the roller
A skydiver jumps out of a helicopter and falls freely for 3 s before opening the parachute.(a) What is the skydiver’s downward velocity when the parachute opens?(b) How far below the helicopter is
A rocket accelerates from rest at a rate of 60 m/s2.(a) What is its speed after it accelerates for 40 s?(b) How long does it take for the rocket to reach a speed of 7,500 m/s?
A runner is going 10 m/s around a curved section of track that has a radius of 35 m. What is the runner’s acceleration?
A child attaches a rubber ball to a string and whirls it around in a circle overhead. If the string is 0.5 m long and the ball’s speed is 10 m/s, what is the ball’s centripetal acceleration?
A high-performance sports car can go from 0 to 100 mph (44.7 m/s) in 7.9 s.(a) What is the car’s average acceleration?(b) The same car can come to a complete stop from 30 m/s in 3.2 s. What is its
How far does a car going 25 m/s travel in 5 s? How far would a jet going 250 m/s travel in 5 s?
A runner in a marathon passes the 5-mile mark at 1 o’clock and the 20-mile mark at 3 o’clock. What is the runner’s average speed during this time period?
A passenger jet flies from one airport to another 1,200 miles away in 2.5 h. Find its average speed.
A hypnotist’s watch hanging from a chain swings back and forth every 0.8 s. What is the frequency of its oscillation?
A convenient time unit for short time intervals is the millisecond. Express 0.0452 s in milliseconds.
A yacht is 20 m long. Express this length in feet.
Describe the spectrum produced by ionized hydrogen—that is, a sample of hydrogen atoms all of which have lost one electron.
An electron and a proton are moving with the same speed. Which has the longer de Broglie wavelength?
What is the de Broglie wavelength? What happens to the de Broglie wavelength of an electron when its speed is increased?
A high-energy photon can collide with a free electron and give it some energy. (This is called the Compton effect.) How are the photon’s energy, frequency, and wavelength affected by the collision?
The spectrum of light from a star that is observed with the Hubble Space Telescope is not exactly the same as that star’s spectrum observed by a telescope on Earth. Explain why this is so.
If an astronomer examines the emission spectrum from luminous hydrogen gas that is moving away from Earth at a high speed and compares it to a spectrum of hydrogen seen in a laboratory on Earth, what
Compare the emission spectra of the elements hydrogen and helium (Figure 10.12). Which element emits photons of red light that have the higher energy?Figure 10.12 650 750 400 450 500 550 600 700
Discuss what is meant by the term ionization. Give two ways by which an atom might acquire enough energy to become ionized.
What are the basic assumptions of the Bohr model? Describe how the Bohr model accounts for the production of emission-line spectra from elements like hydrogen.
A mixture of hydrogen and neon is heated until it is luminous. Describe what is seen when this light passes through a prism and is projected onto a screen.

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