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college physics reasoning
Questions and Answers of
College Physics Reasoning
Three charges with q = +7.5 ?C are located as shown in Figure P17.21, with L = 25 cm.? (a) What are the magnitude and direction of the total electric force on the charge at the bottom?? (b) What are
The particles in Problem 19 are conducting and are brought together so that they touch. Charge then moves between the two particles so as to make the excess charge on the two particles equal. If the
Two small particles have charges Q1 = +3.0 µC and Q2 = -5.0 µC. If the magnitude of the electric force between the particles is 120 N, what is the distance between the particles?
Three point charges Q1, Q2, and Q3 are arranged to form an equilateral triangle as shown in Figure P17.18. The signs of these charges are unknown. (a) A test charge Qtest is now placed at point
Two point charges are separated by a distance r. If the separation is reduced by a factor of 1.5, by what factor does the electric force between them change?
Two particles of charge Q and 5Q are located as shown in Figure P17.16. When a third charge is placed at the origin, it is found that the force on it is zero. Find a. Figure P17.16 ? y - L· -«L
Four point particles are located at the corners of a square (Fig. P17.15). The two particles on the left each carry a charge +Q. If the electric field at the center of the square is directed to the
A point charge with q1 = +2.5 C is located at x = -3.0 m, y = 0, and a second point charge with q2 = +4.0 C is at x = +1.0 m, y = +2.0 m (Fig. P17.14).? (a) What is the force exerted by q1 on
Which graph in Figure P17.13, a, b, or c, best describes how the electric force between two point charges varies with their separation, r?Figure P17.13 F a
Two particles with electric charges Q and -3Q are separated by a distance of 1.2 m. (a) If Q = 4.5 C, what is the electric force between the two particles? (b) If Q = -4.5 C, how does the
What is the magnitude of the electric force between an electron and a proton in a hydrogen atom? Assume they are point charges separated by 0.050 nm.
What is the magnitude of the electric force between two electrons separated by a distance of 0.10 nm (approximately the diameter of an atom)?
What is the net charge on a Ca+2 ion?
The charge per unit length on a glass rod is λ = -7.5 μC/m. If the rod is 2.5 m long, how many excess electrons are on the rod?
The excess charge per unit area on a surface is σ = -5.0 × 10-3 C/m2. How many excess electrons are there on a 1.0-mm2 piece of the surface?
Approximately how many electrons are in a penny? Assume the penny is made of pure copper.
What is the net charge on an object that has an excess of 45 electrons?
Approximately how many electrons are in your body? What is the total charge of these electrons?
A piece of amber is charged by rubbing with a piece of fur. If the net excess charge on the fur is +8.5 nC (+8.5 × 10-9 C), how many electrons were added to the amber?
You are given a container with 5.0 g of hydrogen atoms. What is the total charge on the electrons in the container? What is the total charge on the protons?
What is the total charge of 1 mole of electrons?
Figure Q17.20 shows the electric field lines outside several Gaussian surfaces, but does not show the electric charges inside. In which cases is the net charge inside positive, negative, or perhaps
An ion is released from rest in a region in which the electric field is nonzero. If the ion moves in a direction anti parallel (opposite) to the direction of the electric field, is the ion positively
The electron was not discovered until well after the laws of electricity were determined. Protons were discovered even later, so scientists such as Coulomb and Gauss did not know that electric charge
A charge is placed inside a partially inflated balloon. If the balloon is then further inflated to a larger volume and the associated surface area increases, does the electric flux though the
Explain why it is desirable that a test charge used to measure a field be small in comparison with the field’s source charge.
Describe at least three ways in which Coulomb’s law is similar to Newton’s law of gravitation. Discuss at least two ways in which the two laws are different.
Explain why the child’s hair in Figure Q17.8 is “standing on end.”Figure Q17.8
In Example 17.1, we mentioned that there are approximately 4 × 1014 atoms in a dust particle of mass 1 ng. Estimate this number for yourself.
When two objects (such as a glass rod and a silk cloth) are rubbed together, electrons can be transferred from one to the other. Can protons also be transferred? Explain why or why not.
Under normal atmospheric conditions, the surface of the Earth is negatively charged. What is the direction of the electric field near the Earth’s surface?
Two point particles, each of charge Q1, are located on the x axis at x = ± L. Another particle having charge Q2 is now placed at the origin. (a) Show that the total force on charge Q2 is
The end of a charged rubber rod will attract small pellets of Styrofoam that, having made contact with the rod, will move violently away from it. Describe why that happens.
The children in Figure Q17.8 are rubbing balloons on their hair and then placing the balloons on the wall and ceiling. If the rubbing process puts excess electrons on the balloon, how does the
If a charged point particle is repelled from a glass rod that has been charged by rubbing with silk, what is the sign of the charge on the particle?
Explain how two objects can be attracted due to an electric force, even when both objects have zero net charge.
Explain how two objects can be attracted due to an electric force, even when one object has zero net charge.
Consider the charges qa, qb, and qc in Figure Q17.3. In terms of magnitude, which charge is the greatest? Which is the smallest? How do you know?Figure Q17.3 Яa 9c Яь.
Determine the sign of each charge qa, qb, and qc in Figure Q17.3. Яa 9b
Suppose (hypothetically) that two electric field lines crossed. What would that mean for a test charge placed at the crossing point? Use your result to explain why two electric field lines cannot
When a glass rod is rubbed with silk, the rod becomes positively charged, but when a rubber rod is rubbed with fur, the rubber becomes negatively charged. Suppose you have a charged object but
Consider a steel rod of diameter 1.0 cm and length 1.0 m. If the temperature of this rod is increased by 25°C, its length will change by a certain amount ΔL. The length can also be changed by
A carpenter constructs a house of length 15 m out of wood. If the temperature changes by 5.0°C, how much does the length of the house change?
The author’s gold wedding ring is stuck on his finger, and he must remove it. The ring has an inside diameter of 2.00 cm, but the knuckle of the finger in question has a diameter of 2.05 cm. The
When the metal cap on a glass jar is stuck (i.e., when the cap is too tight to open), it sometimes helps to hold the jar and cap under hot water. Explain why.
The pressure amplitude associated with a very faint sound is about 2 × 10-5 Pa. (a) If this is the difference in pressure between the two sides of your eardrum, what is the approximate force on
Figure P22.78 (left) shows an AC voltage source connected to a capacitor. The graphs on the right show the current as a function of time for two values of the capacitance C1 and C2. What is the
Figure P22.79 (left) shows an AC voltage source connected to an inductor. The graphs on the right show the current as a function of time for two values of the inductance L1 and L2. What is the
Magnetic induction is used to provide real-time amplifi cation to hearing-impaired audience members. The system taps into the amplifi cation system already in place in the room and routes the amplifi
The phenomenon of resonance makes it possible to listen to AM broadcasts with a very simple circuit and never need a battery. When a system is driven at its resonant frequency, even if by minute
Copper telephone wires were originally designed to carry “commercial speech” using a band of frequencies from 300 Hz to 3400 Hz through a system called the PSTN (Public Switched Telephone
The power brick for the author’s laptop computer (Fig. 22.30) has the following power specifications: AC 100 V/1.6 A; DC 16.5 V/3.6 A. Here, the numbers following “AC” describe the input to the
On a hot summer day, an electric fan can make a difference in comfort. The fan does not cool the air, however. In fact, it slightly raises the temperature of the air that it circulates. How is it
Consider Joule’s experiment described in Insight 14.1. Assume the mass m = 2.0 kg and the fluid is water with a volume of 1.0 L. What is the increase in the temperature of the water when the mass
Metal cookware made from steel or aluminum often has a copper bottom. Why?
Why does a lake freeze first at its surface?
You are a high-precision carpenter and use a high-precision steel ruler. If you want the dimensions of your work to be accurate to 1.0 mm over distances of 15 m, you will have to keep the temperature
There are many different types of glass; all are composed mainly of SiO2, but the addition of other elements can change the color and other properties substantially. One type of glass, called Pyrex,
A cup of coffee is initially at a temperature of 70°C and then cools to room temperature. (a) Estimate how much heat flows out of the cup during this time. (b) If this energy were
A potato will bake faster if a nail is stuck through it. Why? Which would make the potato cook faster, an aluminum nail or a steel nail?
You are a blacksmith and have been working with 12 kg of steel. When you are finished shaping it, the steel is at a temperature of 400°C. To cool it off, you drop it into a bucket containing 5.0 kg
You are a blacksmith and have been working with 12 kg of steel. When you are finished shaping it, the steel is at a temperature of 400°C. To cool it off, you drop it into a bucket containing 5.0 kg
(a) How much energy is required to evaporate all the water in a swimming pool of area 100 m2 and depth 2.0 m on a typical summer day?(b) The intensity of sunlight is about 1000 W/m2. If all this
One section of a steel railroad track is 25 m long. If its temperature increases by 25 K during the day, how much does the track expand?
One section of a steel railroad track is 25 m long. If its temperature increases by 25 K during the day, how much does the track expand?
A material of unknown composition with an initial length of 2.0 m is found to expand by 0.33 mm when it is heated by 15 K. What is the coefficient of thermal expansion of this material?
A new cement bridge will be 50 m long. The bridge contains expansion joints, so it will not crack when the temperature changes. Suppose you are the designer of this bridge, and your job is to design
A new cement bridge will be 50 m long. The bridge contains expansion joints, so it will not crack when the temperature changes. Suppose you are the designer of this bridge, and your job is to design
A material of unknown composition with an initial length of 2.0 m is found to expand by 0.33 mm when it is heated by 15 K. What is the coefficient of thermal expansion of this material?
Your swimming pool is square and 5.0 m on a side. It is 3.0 m deep in the morning. If the temperature changes by 20°C during the afternoon, how much does the depth of the water increase?
The Golden Gate Bridge is a famous suspension bridge in San Francisco. The main segment is approximately 1400 m long and is composed of steel. Estimate how much the length of the bridge increases as
The Golden Gate Bridge is a famous suspension bridge in San Francisco. The main segment is approximately 1400 m long and is composed of steel. Estimate how much the length of the bridge increases as
Your swimming pool is square and 5.0 m on a side. It is 3.0 m deep in the morning. If the temperature changes by 20°C during the afternoon, how much does the depth of the water increase?
A steel building is 120 m tall when the outside temperature is 0°C. How tall is the building on a hot summer day (30°C)? The change in height is small, so express your answer with five significant
A steel building is 120 m tall when the outside temperature is 0°C. How tall is the building on a hot summer day (30°C)? The change in height is small, so express your answer with five significant
You are given the job of designing a bridge that is to be made of concrete slabs that rest on a steel support frame. The total length of the bridge is 300 m, and you want to be sure that the
You are given the job of designing a bridge that is to be made of concrete slabs that rest on a steel support frame. The total length of the bridge is 300 m, and you want to be sure that the
A blood flow meter uses the Doppler effect to measure the speed of blood. Suppose a sound wave at 80,000 Hz is emitted into a vein where the speed of sound is about 1500 m/s. The wave is
Two adjacent notes in the musical scale used in Western music have fundamental frequencies whose ratio is approximately 1.059. For example, the fundamental frequencies of the notes C-sharp and C have
A trumpet at room temperature (25°C) is tuned to play the note middle C, which has a fundamental frequency of 262 Hz. The trumpet is then taken outside, and after a few minutes, it is found that the
Dolphins use sonar as a sixth sense, giving them a three dimensional view of their surroundings via sound. A dolphin’s hearing spans the range from 15 Hz to 150 kHz, making use of the 75–110 kHz
You buy a dog whistle that operates at 21 kHz, but when you blow into it, your dog does not show the slightest reaction. You decide to see if you can hear the whistle yourself. Two friends help you.
On a summer afternoon, a pipe that is open at both ends is held vertically with one end submerged in water as shown in Figure P13.70. If a 220-Hz tuning fork is held over the end of the tube, it
The lowest frequency an average human ear can perceive is about 15 Hz, and the highest about 18 kHz. How tall would an organ pipe have to be to produce the lowest note? How short a tube would be
Consider the falling tuning fork in Problem 68 with frequency 440 Hz. (a) You hear it splash into the water at the bottom of the well after 1.8 s. How deep is the well? (b) What frequency
Drop in pitch. A tuning fork that rings at 440 Hz is dropped down a deep well. How far down the well is the fork when the pitch is at 425 Hz? Don’t forget to include the time it takes the sound to
The sound of the talking or singing voice is produced by the vocal cords together with the vocal tract. When air is expelled through your throat, the vocal cords vibrate. For an adult man, this
While taking a walk around your neighborhood, you see a flash of lightning hit the Earth in the distance. You immediately look at your watch and then hear thunder approximately 9 s later. (a)
The human ear canal (Fig. 13.3) is typically about 2.4 cm long, is roughly cylindrical, and is closed at one end where it is capped by the eardrum.? (a) What is the fundamental frequency of the ear
A child drops a rock into a vertical mine shaft that is precisely 406 m deep. The sound of the rock hitting the bottom of the shaft is heard 10.3 s after the child drops the rock. What is the
Some climate data suggest that during the period 1950 to 2000, the Earth’s surface warmed an average of about 1°C. If the oceans have warmed this amount, how much will this change the time it
An ambulance with a siren emitting a whine at 1200 Hz overtakes and passes a cyclist pedaling a bike at 2.5 m/s. After being passed, the cyclist hears a frequency of 980 Hz. How fast is the ambulance
Two identical police cars are chasing a robber. When at rest, their sirens have a frequency of 500 Hz. A stationary observer watches as the two cars approach. The siren of one car (car 1) has a
Consider again the insect in Problem 58. If the insect moves the 10-cm distance in 0.50 s, what is the magnitude of the Doppler shift in the bat’s reflected sound wave? Assume the insect is moving
A bat is pursuing an insect and using echolocation of 60-kHz sound waves to track the insect. The insect is initially 30 cm from the bat, but then moves to a distance of 40 cm as it tries to escape.
The siren in an ambulance has a frequency (according to you) of 1100 Hz as it moves toward you at speed v. It then makes a U-turn and travels away from you with speed v, and you hear a frequency of
A siren is approaching you at 35 m/s and is perceived to have a frequency of 1100 Hz. If the siren stops moving, what frequency do you now hear?
A guitar is tuned to play a note at 440 Hz. If the guitar is in a moving car and the note has a perceived frequency of 410 Hz, what is the speed of the car? Assume the car is moving directly away
A siren has a frequency of 950 Hz when it and an observer are both at rest. The observer then starts to move and finds that the frequency he hears is 1000 Hz. (a) Is the observer moving toward
A siren has a frequency of 750 Hz when it is at rest, whereas it has an apparent frequency of 800 Hz when it is moving toward a stationary observer. What is the speed of the siren in the latter case?
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