Question: In a circus trapeze act, two acrobats

> A lightweight plastic rod is rubbed with a piece of fur. A second plastic rod, hanging from a string, is attracted to the first rod and swings toward it. When the second rod touches the first, it is suddenly repelled and swings away. Explain what has hap

> Your laboratory partner hands you a glass rod and asks if it has negative charge on it. There is an electroscope in the laboratory. How can you tell if the rod is charged? Can you determine the sign of the charge? If the rod is charged to begin with, wil

> Many real estate agents have an ultrasonic rangefinder that enables them to quickly and easily measure the dimensions of a room. The device is held to one wall and reads the distance to the opposite wall. How does it work?

> A spring scale in a French market is calibrated to show the mass of vegetables in grams and kilograms. (a) If the marks on the scale are 1.0 mm apart for every 25 g, what maximum extension of the spring is required to measure up to 5.0 kg? (b) What is

> Suppose that a string of length L and mass m is under tension F. (a) Show that has units of speed. (b) Show that there is no other combination of L, m, and F with units of speed. [Hint: Of the dimensions of the three quantities L, m, and F, only F in

> Crocodiles are thought to be able to detect changes in the flux due to Earth’s magnetic field as they move their heads. Suppose a crocodile is initially facing north. The horizontal component of Earth’s magnetic field is 30 μT. Consider a vertical, circu

> Suppose that as you travel away from Earth in a spaceship, you observe another ship pass you heading in the same direction and measure its speed to be 0.50c. As you look back at Earth, you measure Earth's speed relative to you to be 0.90c. What is the sp

> A rod is negatively charged by rubbing it with fur. It is brought near another rod of unknown composition and charge. There is a repulsive force on each. (a) Is the first rod an insulator or a conductor? Explain. (b) What can you tell about the charge o

> An object has a mass of 12.6 kg and a speed of 0.87c. (a) What is the magnitude of its momentum? (b) If a constant force of 424.6 N acts in the direction opposite to the object's motion, how long must the force act to bring the object to rest? [Hint: U

> The time to sunset can be estimated by holding out your arm with your fingers perpendicular to the path the Sun will follow to the horizon. The number of fingers that fit between the Sun and the sunset point is proportional to the time remaining. (a) Wh

> A concave mirror has focal length f. (a) If you look into the mirror from a distance less than f, is the image you see upright or inverted? (b) If you stand at a distance greater than 2f, is the image upright or inverted? (c) If you stand at a distance

> What happens if a 40 W incandescent lightbulb, designed to be connected to an ac voltage with amplitude 170 V and frequency 60 Hz, is instead connected to a 170 V dc power supply? Explain. What dc voltage would make the lightbulb burn with the same brigh

> A hedge trimmer has a blade that moves back and forth with a frequency of 28 Hz. The blade motion is converted from the rotation of an electric motor to oscillatory motion by means of a Scotch yoke (see Conceptual Question 7). The blade moves 2.4 cm from

> Why does the resistivity of a metallic conductor increase with increasing temperature?

> Electronic devices are usually enclosed in metal boxes. One function of the box is to shield the inside components from external electric fields. (a) How does this shielding work? (b) Why is the degree of shielding better for constant or slowly varying

> When a proton and an antiproton annihilate, the annihilation products are usually pions. (a) Suppose three pions are produced. What combination(s) of π+, π−, and π0 are possible? (b) Suppose five pions are produced. What combination(s) of π+, π−, and π

> A particle decays in flight into two pions, each having a rest energy of 140.0 MeV. The pions travel at right angles to each other with equal speeds of 0.900c. Find (a) the momentum magnitude of the original particle, (b) its kinetic energy, and (c) i

> A roller coaster car of mass 320 kg (including passengers) travels around a horizontal curve of radius 35 m. Its speed is 16 m/s. (a) What are the magnitude and direction of the total force exerted on the car by the track? (b) What is the banking angle

> In this problem, use Ampere's law to show that the magnetic field inside a long solenoid is B = μ0nI. Assume that the field inside the solenoid is uniform and parallel to the axis and that the field outside is zero. Choose a rectangular pat

> A 2.0 kg object is at rest on a frictionless surface when it is hit by a 3.0 kg object moving at 8.0 m/s. If the two objects are stuck together after the collision, what is the speed of the combination?

> A mass-and-spring system oscillates with amplitude A and angular frequency ω. (a) What is the average speed during one complete cycle of oscillation? (b) What is the maximum speed? (c) Find the ratio of the average speed to the maximum speed. (d) Ske

> A metal sphere is initially uncharged. After being touched by a charged rod, the metal sphere is positively charged. (a) Is the mass of the sphere larger, smaller, or the same as before it was charged? Explain. (b) What sign of charge is on the rod?

> A road with a radius of 75.0 m is banked so that a car can navigate the curve at a speed of 15.0 m/s without any friction. On a cold day when the street is icy, the coefficient of static friction between the tires and the road is 0.120. What is the slowe

> A horizontal spring with spring constant of 9.82 N/m is attached to a block with a mass of 1.24 kg that sits on a frictionless surface. When the block is 0.345 m from its equilibrium position, it has a speed of 0.543 m/s. (a) What is the maximum displac

> Both a microscope and a telescope can be constructed from two converging lenses. What are the differences? Why can't a telescope be used as a microscope? Why can't a microscope be used as a telescope?

> A battery has a terminal voltage of 12.0 V when no current flows. Its internal resistance is 2.0 Ω. If a 1.0 Ω resistor is connected across the battery terminals, what is the terminal voltage and what is the current through the 1.0 Ω resistor?

> A high-speed dental drill is rotating at 3.14 × 104 rad/s. Through how many degrees does the drill rotate in 1.00 s?

> Can an astronaut on the Moon use a straw to drink from a normal drinking glass? How about if he pokes a straw through an otherwise sealed juice box? Explain.

> Explain how it is possible that more than half of the molecules in an ideal gas have kinetic energies less than the average kinetic energy. Shouldn't half have less and half have more?

> The sound level 25 m from a loudspeaker is 71 dB. What is the rate at which sound energy is produced by the loudspeaker, assuming it to be an isotropic source?

> A straight, stiff wire of length 1.00 m and mass 25 g is suspended in a magnetic field B = 0.75 T. The wire is connected to an emf. How much current must flow in the wire and in what direction so that the wire is suspended and the tension in the supporti

> A sound wave in room-temperature air has an intensity level of 65.0 dB and a frequency of 131 Hz. (a) What is the pressure amplitude? (b) What is the displacement amplitude?

> A bicycle and its rider together have a mass of 75 kg. What power output of the rider is required to maintain a constant speed of 4.0 m/s (about 9 mi/h) up a 5.0% grade (a road that rises 5.0 m for every 100 m along the pavement)? Assume that frictional

> In the figure, switch S is initially open. It is closed, and then opened again a few seconds later. (a) In what direction does current flow through the ammeter when switch S is closed? (b) In what direction does current flow when switch S is then opene

> What is the mass of one gold atom in kilograms?

> A circuit has a resistor and an unknown component in series with a 12 V (rms) sinusoidal ac source. The current in the circuit decreases by 20% when the frequency decreases from 240 Hz to 160 Hz. What is the second component in the circuit? Explain your

> Two speakers spaced a distance 1.5 m apart emit coherent sound waves at a frequency of 680 Hz in all directions. The waves start out in phase with each other. A listener walks in a circle of radius greater than 1 m centered on the midpoint of the two spe

> 1. An electron, passing close to a target nucleus, slows and radiates away some of its energy. What is this process called? (a) Compton effect (b) photoelectric effect (c) bremsstrahlung (d) blackbody radiation (e) stimulated emission 2. How many emissi

> A pendulum is made from a uniform rod of mass m1 and a small block of mass m2 attached at the lower end. (a) If the length of the pendulum is L and the oscillations are small, find the period of the oscillations in terms of m1, m2, L, and g. (b) Check

> Explain why electric field lines begin on positive charges and end on negative charges. [Hint: What is the direction of the electric field near positive and negative charges?]

> A biologist is studying plant growth and wants to simulate a gravitational field twice as strong as Earth’s. She places the plants on a horizontal rotating table in her laboratory on Earth at a distance of 12.5 cm from the axis of rotat

> Explain why any net charge on a solid metal conductor in electrostatic equilibrium is found on the outside surface of the conductor instead of being distributed uniformly throughout the solid.

> What makes clothes cling together—or to your body—after they’ve been through the dryer? Why do they not cling as much if they are taken out of the dryer while slightly damp? In which case would you expect your clothes to cling more, all other things bein

> A wooden barrel full of water has a flat circular top of radius 25.0 cm with a small hole in it. A tube of height 8.00 m and inner radius 0.250 cm is suspended above the barrel with its lower end inserted snugly in the hole. Water is poured into the uppe

> Two children are playing with a tin-can telephone. The children are 12 m apart, the string connecting their tin cans has a linear mass density of 1.3 g/m, and it is stretched with a tension of 8.0 N. One child decides to pluck the string. How long does i

> A proposed “space elevator” consists of a cable going all the way from the ground to a space station in geostationary orbit (always above the same point on Earth’s surface). Elevator “cars” would climb the cable to transport cargo to outer space. Conside

> A convex mirror produces an image located 18.4 cm behind the mirror when an object is placed 32.0 cm in front of the mirror. What is the focal length of this mirror?

> At t = 0, six birds are flying south at 10 m/s. Their masses and their velocities at a later time are: (a) 200 g, 10 m/s north at t = 30 s (b) 200 g, 10 m/s east at t = 30 s (c) 200 g, 20 m/s north at t = 60 s (d) 400 g, 20 m/s north at t = 60 s (e) 400

> A cup of hot coffee has been poured, but the coffee drinker has a little more work to do at the computer before she picks up the cup. She intends to add some milk to the coffee. To keep the coffee hot as long as possible, should she add the milk at once,

> Two factors that can determine the distance over which a force can act are the mass of the exchange particle that carries the force and the Heisenberg uncertainty principle [Eq. (28-5)]. Assume that the uncertainty in the energy of an exchange particle i

> When the temperature as measured in °C of a radiating object is doubled (such as a change from 20°C to 40°C), is the radiation rate necessarily increased by a factor of 16?

> A 5.0 mH inductor and a 10.0 Q resistor are connected in series with a 6.0 V dc battery. (a) What is the voltage across the resistor immediately after the switch is closed? (b) What is the voltage across the resistor after the switch has been closed fo

> At very low temperatures, the molar specific heat of hydrogen (H2) is CV = 1.5R. At room temperature, CV = 2.5R. Explain.

> Calculate the value of (a) Planck's constant and (b) the work function of the metal from the data obtained by Robert A. Millikan in 1916, as shown in the graph. Millikan was attempting to disprove Einstein's photoelectric equation; instead he found tha

> Explain why two waves of significantly different frequencies cannot be coherent.

> Medical testing has established that the maximum acceleration a pilot can be subjected to without losing consciousness is approximately 5.0g if the axis of acceleration is aligned with the spine. (See Example 5.4.) A pilot can avoid “blackout” at acceler

> Why can a neutron within a nucleus be stable, whereas an isolated neutron is unstable? What determines whether a neutron within a nucleus is stable? [Hint: Consider conservation of energy.]

> At what time is the current in the inductor 0.0010 times its initial value?

> A spy satellite is in circular orbit around Earth. It makes one revolution in 6.00 h. (a) How high above Earth’s surface is the satellite? (b) What is the satellite’s acceleration?

> A velodrome is built for use in the Olympics. The radius of curvature of the surface is 20.0 m. At what angle should the surface be banked for cyclists moving at 18 m/s? (Choose an angle so that no frictional force is needed to keep the cyclists in their

> A square loop of wire, 0.75 m on each side, has one edge along the positive z-axis and is tilted toward the yz-plane at an angle of 30.0° with respect to the horizontal (xz-plane). There is a uniform magnetic field of 0.32 T pointing in the po

> Explain why the molar specific heat of a diatomic gas such as O2 is larger than that of a monatomic gas such as Ne.

> A room air conditioner causes a temperature change of −6.0°C. (a) What is the temperature change in kelvins? (b) What is the temperature change in °F?

> Repeat Problem 37 for an operating frequency of 98.7 Hz. (a) What is the phase angle for this circuit? (b) Draw the phasor diagram. (c) What is the resonant frequency for this circuit?

> Approximately what is the total energy of the neutrino emitted when / decays by electron capture?

> While an elevator of mass 2530 kg moves upward, the tension in the cable is 33.6 kN. (a) What is the acceleration of the elevator? (b) If at some point in the motion the velocity of the elevator is 1.20 m/s upward, what is the elevator’s velocity 4.00 s

> An electric mixer is being used to mix up some cake batter. What happens to the motor if the batter is too thick, so the beaters are turning slowly?

> In Section 25.3 we studied interference due to thin films. Why must the film be thin? Why don't we see interference effects when looking through a window or at a poster covered by a plate of glass—even if the glass is optically flat?

> Can sound waves be polarized? Explain.

> An electron (charge −e) is projected horizontally into the space between two oppositely charged parallel plates. The electric field between the plates is 500.0 N/C upward. If the vertical deflection of the electron as it leaves the plates has magnitude 3

> Think of a wire of length L as two wires of length L/2 in series. Construct an argument for why the resistance of a wire must be proportional to its length.

> A battery is connected to a clock by copper wires as shown. What is the direction of current through the clock (B to C or C to B)? What is the direction of current through the battery (D to A or A to D)? Which terminal of the battery is at the higher pot

> Some batteries can be “recharged.” Does that mean that the battery has a supply of charge that is depleted as the battery is used? If “recharging” does not literally mean to put char

> To resolve details of a cell using an ordinary microscope, you must use a wavelength that is about the same size, or smaller, than the details of the cell you want to observe. Suppose you want to be able to see the ribosomes, which are about 20 nm in dia

> In this problem, you will estimate the smallest kinetic energy of vibration that the human ear can detect. Suppose that a harmonic sound wave at the threshold of hearing (I = 1.0 × 10−12 W/m2) is incident on the eardrum. Take the speed of sound as 340 m/

> 11. An object is in nonuniform circular motion with constant angular acceleration. Identify the correct statement(s). (Use the same answer choices as in Question 10.) (a) 1 only (b) 2 only (c) 3 only (d) 1, 2, and 3 (e) 2 and 3 (f) 1 and 2 (g) 1 and 3 (h

> A motorist driving a 1200 kg car on level ground accelerates from 20.0 m/s to 30.0 m/s in a time of 5.0 s. Ignoring friction and air resistance, determine the average mechanical power in watts the engine must supply during this time interval.

> A parallel plate capacitor has a charge of 0.020 µC on each plate with a potential difference of 240 V. The parallel plates are separated by 0.40 mm of air. (a) What is the capacitance for this capacitor? (b) What is the area of a single plate? (c) At

> When the viola section of an orchestra with six members plays together, is the sound 6 times as loud as when a single viola plays? Explain. Is the intensity 6 times what it would be for a single viola? [Hint: The six sound waves are not coherent.]

> Why don't you see an interference pattern on your desk when you have light from two different lamps illuminating the surface?

> Derivation of the Doppler formula for light. A source and observer of EM waves move relative to each other at velocity v. Let v be positive if the observer and source are moving apart from each other. The source emits an EM wave at frequency fs (measured

> A pion (mass 0.140 GeV/c2) at rest decays by the weak interaction into a muon of mass 0.106 GeV/c2 and a muon antineutrino: What is the total kinetic energy of the muon and the antineutrino?

> A spring of negligible mass is compressed between two blocks, A and B, which are at rest on a frictionless horizontal surface at a distance of 1.0 m from a wall on the left and 3.0 m from a wall on the right. The sizes of the blocks and spring are small.

> A variable capacitor is made of two parallel semicircular plates with air between them. One plate is fixed in place and the other can be rotated. The electric field is zero everywhere except in the region where the plates overlap. When the plates are dir

> What is the average linear speed of Earth about the Sun?

> A 1500 kg car coasts in neutral down a 2.0° hill. The car attains a terminal speed of 20.0 m/s. (a) How much power must the engine deliver to drive the car on a level road at 20.0 m/s? (b) If the maximum useful power that can be delivered by the engine

> The figure shows standing wave patterns in five pipes of equal length. Pipes (c) and (e) are open at both ends; the others are closed at one end. Rank the standing waves in order of the frequency, largest to smallest.

> Rhonda keeps a 2.0 kg model airplane moving at constant speed in a horizontal circle at the end of a string of length 1.0 m. The tension in the string is 18 N. How much work does the string do on the plane during each revolution?

> A charged pion can decay either into a muon or an electron. The two decay modes of a π− are: / And / . Write the two decay modes for the π+. [Hint: π+ is the antiparticle of π−. Replace each particle in the decay reaction with its corresponding antipa

> A coil of wire is connected to an ideal 6.00 V battery at t = 0. At t = 10.0 ms, the current in the coil is 204 mA. One minute later, the current is 273 mA. Find the resistance and inductance of the coil. [Hint: Sketch I(t).]

> A police car’s radar gun emits microwaves with a frequency of f1 = 36.0 GHz. The beam reflects from a speeding car, which is moving away at 43.0 m/s with respect to the police car. The frequency of the reflected microwave as observed by the police is f2.

> A bicycle wheel, of radius 0.30 m and mass 2 kg (concentrated on the rim), is rotating at 4.00 rev/s. After 50 s the wheel comes to a stop because of friction. What is the magnitude of the average torque due to frictional forces?

> A spherical balloon with a radius of 12.0 cm is filled with helium. The bottom of the balloon is attached to a 2.30 m length of ribbon that is anchored to the ground. The balloon alone has a mass of 2.80 × 10−3 kg. Ignore the mass of the ribbon. (a) Wha

> The figure shows a magnetic dipole antenna transmitting an electromagnetic wave. At a point P far from the antenna, what are the directions of the electric and magnetic fields of the wave?

> A bird perched on a power line is not harmed, but if you are pruning a tree and your metal pole saw comes in contact with the same wire, you risk being electrocuted. Explain.

> A negatively charged particle of mass 5.00 × 10−19 kg is moving with a speed of 35.0 m/s when it enters the region between two parallel capacitor plates. The initial velocity of the charge is parallel to the plate surfaces

> When a coin is tossed directly upward, what can you say about its velocity and acceleration at the high point of the toss?

> A container is filled with gas at a pressure of 4.0 × 105 Pa. The container is a cube, 0.10 m on a side, with one side facing south. What is the magnitude and direction of the force on the south side of the container due to the gas inside?

> A fisherman notices a buoy bobbing up and down in the water in ripples produced by waves from a passing speedboat. These waves travel at 2.5 m/s and have a wavelength of 7.5 m. At what frequency does the buoy bob up and down?

> An RLC circuit has a resistance of 10.0 Ω, an inductance of 15.0 mH, and a capacitance of 350 µF. By what factor does the impedance of this circuit change when the frequency at which it is driven changes from 60 Hz to 120 Hz? Does the impedance increase