Questions and Answers of Inquiry into Physics

In what way(s) is Einstein’s general theory of relativity superior to Newton’s theory of universal gravitation? Give an example of a case where Einstein’s theory provides a more accurate
After landing on the planet Mars, two astronauts awaken from a long induced hibernation inside their windowless spacecraft. Before emerging, is there any way they can determine whether their
The principle of equivalence underlies the general theory of relativity. What does this principle assert about the motion of objects in a uniform gravitational field?
Given the Newtonian view of gravity, why is it reasonable to expect that the rate at which the universe is expanding should be decreasing with time? Do observations of the motions of remote galaxies
If a horseshoe is heated in a blacksmith’s furnace until it glows red hot, does the mass of the horseshoe change? If a spring is stretched to twice its equilibrium length, has its mass been altered
Does E0 = mc2 apply only to objects traveling at the speed of light? Why or why not?
Newton wrote: “Absolute, true, and mathematical time, of itself, and from its own Nature, flows equally without relation to anything external.” Comment on the significance of this statement for
Galileo used his pulse like a clock to measure time intervals by counting the number of heartbeats. If Galileo were traveling in a spaceship, moving uniformly at a speed near that of light, would he
In your own words, define what is meant by time dilation in special relativity theory. Provide a similar definition for length contraction. Give an example in which the effects of time dilation are
Light travels in water at a speed of 2.25 x 108 m/s. Is it possible for particles to travel through water at a speed ν > 2.25 x 108 m/s? Why or why not? Explain.
Suppose you were traveling toward the Sun at a constant velocity of 0.25c. With what speed does the light streaming out from the Sun go past you? Explain your reasoning.
Describe the two fundamental postulates underlying Einstein’s special theory of relativity.
What does the acronym PET stand for? Why is PET a good example with which to begin a discussion of elementary particle physics?
Figure 12.35 shows the appearance of three spherical space pods as seen by an Earth-bound observer. The pods are traveling along the same direction, but have different speeds relative to the
Describe the role of inflation in cosmology. How does it help to explain why the geometry of the universe is flat? What is the source of the energy that drove the rapid expansion of the universe
What is dark energy and what role does it play in our understanding of The structure and evolution of the universe?
What is dark matter and how much of the total massenergy budget of the universe consists of dark matter? Give two dark matter candidates that have been proposed by particle physicists.
If a proton can decay, then its lifetime is of the order of 1034 years, far longer than the current age of the universe. Does this necessarily imply that a proton decay has not yet occurred in the
Unification of its basic laws and theories has long been a goal in physics. Describe some ways in which physicists have been successful in unifying certain forces and theories. In what area(s) of
A bumper “snicker” on a car belonging to the chairperson of a physics department reads: “Particle physicists have GUTs!” Explain in your own words the meaning of this little joke or “play
Describe the Standard Model of elementary particle physics.
Quarks are said to possess “color.” What does this mean? Are physicists really suggesting that quarks look red like ripe strawberries or blue like the cloudless daytime sky? Explain.
What kind of a particle (baryon, meson, or lepton) corresponds to a tt̅—that is, to a top-antitop quark combination? Describe some of the properties such a particle would have.
In the quark model, is it possible to have a baryon with strangeness -1 and electric charge +2? Explain.
Show that time stands still at the Schwarzschild radius of a black hole. Specifically, demonstrate that Dtf → ∞ when d = dS in the time dilation equation for any value of Dtd. The implications of
If the average lifetime of a proton was 1033 years, about how many protons would you have to assemble together and observe simultaneously to witness a total of 100 proton decays in one year? Explain
The F- meson possesses -1 unit of charge, -1 unit of strangeness, and -1 unit of charm. Identify the quark combination making up this rare subatomic particle.
Distinguish a particle composed of a combination of d̅ u̅ s̅ quarks from one composed of dus quarks in as many ways as you can. Do the same for a dss combination and a d̅ s̅ s̅
Give three (3) combinations of quarks (not antiquarks!) that will give baryons with charge: (a) +1; (b) -1;(c) 0.
A 0.1-kg ball connected to a fixed point by a taut string whirls around a circular path of radius 0.5 m at a speed of 3 m/s. Find the angular momentum of the orbiting ball. Compare this with the
Sirius B has a mass and radius of 2.1 x 1030 kg and 5.5 x 106 m, respectively. Assuming Sirius B is perfectly spherical in shape, compute the ratio of the Δtf t / Δtd. Using this result, confirm
How many years would you have to wait to observe a 1° angular shift in the perihelion of Mercury due to general relativistic effects?
Determine the redshift of a photon whose observed wavelength is 656.9 nm if its emitted wavelength is 656.3 nm.
If the relativistic kinetic energy of a particle is 9 times its rest energy, at what fraction of the speed of light must the particle be traveling?
The tau is the heaviest of all the known leptons, having a mass of 1,777 MeV/c2. Find the rest energy of a tau in MeVs and joules. What is the mass of the tau in kilograms? Compare your result with
If an electron is speeding down the two-mile-long Stanford Linear Accelerator at 99.98 percent the speed of light, how many meters long is the trip as seen from the perspective of the electron?
A computer in a laboratory requires 2.50 μs to make a certain calculation, as measured by a scientist in the lab. To someone moving past the lab at a relative speed of 0.995c, how long will the same
How fast would a muon have to be traveling relative to an observer for its lifetime as measured by this observer to be 10 times longer than its lifetime when at rest relative to the observer?
The concept of a black hole, that is, an object whose gravity is so strong that not even light, traveling at a speed of 3 x 108 m/s, can escape from it, dates back to at least the 18th century and
Suppose you perform a scattering experiment in which you fire BBs into a slab of jello in which a layer of randomly distributed but identical marbles are suspended. Of the BBs entering the jello, 90
One interesting (unbelievable?) implication of time dilation is contained in what is called the twin paradox. Imagine identical twins who decide to perform an experiment to test the accuracy of
In the electroweak theory, symmetry breaking occurs on a length scale of about 10-17 m. Compute the frequency of particles with de Broglie wavelengths (see Section 10.5) equal to this value, and,
Although doubly charged baryons have been found (baryons with net charge 12), no doubly charged mesons have yet been identified. What effect on the quark model would there be if a meson of charge 12
If the average lifetime of the proton were 1016 years, estimate the number of protons per kilogram of human body mass that would decay radioactively each year. Assume that a human being is made
When a proton–antiproton pair at rest annihilates, two photons are created. Find the wavelengths of these two light quanta, given that they share equally in the annihilation energy. In what portion
Compare the strength of the electric force to that of the gravitational force as suggested in Section 12.3. In particular, find the ratio of the Coulomb force of repulsion between two protons
Show that in the limit of low speeds the expression for the relativistic kinetic energy (see Important Equations) reduces to the familiar one from classical mechanics, KE = (1/2)mv2.
A 3,000-kg truck runs into the rear of a 1,000-kg car that was stationary. The truck and car are locked together after the collision and move with speed 9 m/s. What was the speed of the truck before
If we know that a force of 5 N acts on an object while it moves 2 meters, can we calculate how much work was done with no other information? Explain.
The work-energy theorem: Show explicitly that the work, Fd, done by a constant force to accelerate an object of mass m from rest to a final velocity v is equal to the kinetic energy, (1/2)mv2, of the
At the point in its orbit when it is closest to the Sun, Halley€™s Comet moves with a speed of 54,500 m/s (Figure 3.48). When it is at its most distant point, the separation between it and
Describe several things you have done today that involved doing work. Are you doing work right now?
The “shot” used in the shot-put event is a metal ball with a mass of 7.3 kg. When thrown in Olympic competition, it is accelerated to a speed of about 14 m/s. As an approximation, let’s say
A basketball with a mass of 0.62 kg falls vertically to the floor where it hits with a speed of −6 m/s. (We take the positive direction to be upward here.) The ball rebounds, leaving the floor with
For what type of interaction between bodies is the law of conservation of linear momentum most useful?
Assume that as a car brakes to a stop it undergoes a constant acceleration (deceleration). Explain why the stopping distance becomes four times as large if the initial speed is doubled.
An astronaut working with many tools some distance away from a spacecraft is stranded when the “maneuvering unit” malfunctions. How can the astronaut return to the spacecraft by sacrificing some
A runner with a mass of 80 kg accelerates from 0 to 9 m/s in 3 s. Find the net force on the runner using the alternate form of Newton’s second law.
A person on a swing moves so that the support rods are horizontal at the turning points (Figure 3.47). Show that the centripetal acceleration of the person at the low point of the arc is exactly 2 g,
Could the linear momentum of a turtle be greater than the linear momentum of a horse? Explain why or why not.
In a head-on, inelastic collision, a 4,000-kg truck going 10 m/s east strikes a 1,000-kg car going 20 m/s west. (a) What is the speed and direction of the wreckage? (b) How much kinetic
Why is the alternate form of Newton’s second law of motion given in this chapter the more general form?
Which has the larger linear momentum: a 2,000-kg houseboat going 5 m/s or a 600-kg speedboat going 20 m/s?
A bullet with a mass of 0.01 kg is fired horizontally into a block of wood hanging on a string. The bullet sticks in the wood and causes it to swing upward to a height of 0.1 m. If the mass of the
What is a conservation law? What is the basic approach taken when using a conservation law?
Re-examine Section 3.3 on work. Make a list of at least 10 key concepts and applications relating to work; write each of the concepts or examples on small Post-it® notes. Rank the items on your list
Rank the following three collisions in terms of the extent of damage that the car would experience. Explain your reasons for ranking the collisions as you did.(a) A car going 10 m/s striking an
A mass of 0.75 kg is attached to a relaxed spring with k 5 2.5 N/m. The mass rests on a horizontal, frictionless surface. If the mass is displaced by 0.33 m, what is the magnitude of the force
A space probe is launched from Earth headed for deep space. At a distance of 10,000 miles from Earth’s center, the gravitational force on it is 600 lb. What is the size of the force when it is at
A centripetal force of 200 N acts on a 1,000-kg satellite moving with a speed of 5,000 m/s in a circular orbit around a planet. What is the radius of its orbit?
A 0.1-kg ball is attached to a string and whirled around in a circle overhead. The string breaks if the force on it exceeds 60 N. What is the maximum speed the ball can have when the radius of the
A race car rounds a curve at 60 m/s. The radius of the curve is 400 m, and the car’s mass is 600 kg.(a) What is the car’s (centripetal) acceleration? What is it in g’s?(b) What is the
An airplane is built to withstand a maximum acceleration of 6 g. If its mass is 1,200 kg, what size force would cause this acceleration?
On aircraft carriers, catapults are used to accelerate jet aircraft to flight speeds in a short distance. One such catapult takes a 18,000-kg jet from 0 to 70 m/s in 2.5 s.(a) What is the
A sprinter with a mass of 80 kg accelerates uniformly from 0 m/s to 9 m/s in 3 s.(a) What is the runner’s acceleration?(b) What is the net force on the runner?(c) How far does the sprinter travel
A jet aircraft with a mass of 4,500 kg has an engine that exerts a force (thrust) equal to 60,000 N.(a) What is the jet’s acceleration when it takes off?(b) What is the jet’s speed after it
During our discussion of the motion of a falling body near Earth’s surface, we said that the gravitational force acting on it—its weight—is constant. But the law of universal gravitation tells
The Kingda Ka roller coaster in New Jersey is the world’s tallest ride of its kind. As the passenger cars are launched from rest at the start, they are accelerated uniformly to a speed of 57 m/s
Complete the calculation of the mass of Earth as outlined in Section 2.7.
A 200-kg communications satellite is placed into a circular orbit around Earth with a radius of 4.23 x 107m (26,300miles).(a) Find the gravitational force on the satellite. (There is some useful
In an experiment performed in a space station, a force of 60 N causes an object to have an acceleration equal to 4 m/s2. What is the object’s mass?
The acceleration of a freely falling body is not exactly the same everywhere on Earth. For example, in the Galapagos Islands at the equator, the acceleration of a freely falling body is 9.780 m/s2,
Perhaps you’ve noticed that the rockets used to put satellites and spacecraft into orbit are usually launched from pads near the equator. Why is this so? Is the fact that rockets are usually
A motorcycle and rider have a total mass equal to 300 kg. The rider applies the brakes, causing the motorcycle to accelerate at a rate of 25 m/s2. What is the net force on the motorcycle?
Perform the calculation of the force acting between two 70-kg people standing 1 m apart to verify the result given in Section 2.7 (3.3 × 1027 N). Show your work.
As a horse and wagon are accelerating from rest, the horse exerts a force of 400 N on the wagon(Figure 2.56). Illustrating Newton€™s third law, the wagon exerts an equal and opposite force
The mass of a certain elephant is 1,130 kg.(a) Find the elephant’s weight in newtons.(b) Find its weight in pounds.
Why does banking a curve on a highway allow a vehicle to successfully negotiate the turn at a higher speed?
Two forces, one equal to 15 N and another equal to 40 N, act on a 50-kg crate resting on a horizontal surface as shown in Figure 2.55.(a) What is the net horizontal force on the crate?(b) What
A child weighs 300 N. What is the child’s mass in kilograms? In slugs?
In this chapter, you’ve encountered a large number of concepts related to forces and motion. Organizing a concept map might help clarify the meanings of many of these concepts for you. As a start,
The force on a baseball as it is being hit with a bat can be more than 8,000 lb. No human can push on a bat with that much force. What is happening in this instance?
Express your weight in newtons. From this determine your mass in kilograms.
Reread Section 2.7 on the law of universal gravitation and make a list of concepts and examples that might serve as a basis for developing a concept map summarizing the material in this section.
During takeoff, an airplane goes from 0 to 50 m/s in 8 s.(a) What is its acceleration?(b) How fast is it going after 5 s?(c) How far has it traveled by the time it reaches 50 m/s?
A rock is dropped off the side of a bridge and hits the water below 2 s later.(a) What was the rock’s velocity when it hit the water?(b) What was the rock’s average velocity as it fell?(c) What
The following data describe different situations where a person is walking or running through a train car while the train is in motion. The speed and direction of motion of the person (P) and the
Draw an accurate graph of the velocity versus time for the elevator inProblem 16. 32 28 24 20 16 12 4 32 12 16 20 24 28 t (seconds) d (meters)
Sketch a graph of velocity versus time for the motion illustrated in Figure 1.24. Indicate what the car€™s acceleration is at different times.Figure 1.24 D B
What does the slope of a distance-versus-time graph represent physically?

Showing 700 - 800 of 843