Questions and Answers of Inquiry into Physics

A running back with a mass of 80 kg and a speed of 8 m/s collides with, and is held by, a 120-kg defensive tackle going in the opposite direction. How fast must the tackle be going before the
Identify as many different forms of energy as you can that are around you at this moment.
When you throw a ball, the work you do to accelerate it equals the kinetic energy the ball gains. If you do twice as much work when throwing the ball, does it go twice as fast? Explain.
Describe the motion of an object that possesses kinetic energy yet undergoes no net displacement.
How can the gravitational potential energy of something be negative?
What is elastic potential energy? Identify some of the things that currently surround you that possess elastic potential energy.
If a spring is compressed to half its length, by how much does the amount of energy stored in the spring change?
As it orbits Earth, the 11,000-kg Hubble Space Telescope travels at a speed of 7,900 m/s and is 560,000 m above Earth’s surface.(a) What is its kinetic energy?(b) What is its potential energy?
Identify the energy conversions taking place in each of the following situations. Name all of the relevant forms of energy that are involved.(a) A camper rubbing two sticks together to start a
Solar-powered spotlights have batteries that are charged by solar cells during the day and then operate lights at night. Describe the energy conversions in this entire process, starting with the
Truck drivers approaching a steep hill that they must climb often increase their speed. What good does this do, if any?
A worker at the top of a 629-m-tall television transmitting tower in North Dakota accidentally drops a heavy tool. If air resistance is negligible, how fast is the tool going just before it hits the
A ball is thrown straight upward from the surface of the Moon. Is the maximum height it reaches less than, equal to, or greater than the maximum height reached by a ball thrown upward on Earth with
Describe the distinction between elastic and inelastic collisions. Give an example of each.
Many sports involve collisions between things—such as balls and rackets—and between people—as in football or hockey. Characterize the various sports collisions as elastic or inelastic.
Carts A and B stick together whenever they collide. The mass of A is twice the mass of B. How could you roll the carts toward each other in such a way that they would be stopped after the collision?
The cliff divers at Acapulco, Mexico, jump off a cliff 26.7 m above the ocean. Ignoring air resistance, how fast are the divers going when they hit the water?
Is it possible for one object to gain mechanical energy from another without touching it? Explain.
How are the physical concepts power and speed similar?
The fastest that a human has run is about 12 m/s.(a) If a pole vaulter could run this fast and convert all of her kinetic energy into gravitational potential energy, how high would she go?(b) Compare
Two cranes are lifting identical steel beams at the same time. One crane is putting out twice as much power as the other. Assuming friction is negligible, what can you conclude is happening to
A person runs up several flights of stairs and is exhausted at the top. Later, the same person walks up the same stairs and does not feel as tired. Why is this? Ignoring air resistance, does it take
In January 2003, an 18-year-old student gained a bit of fame for surviving—with only minor injuries—a remarkable traffic accident. The vehicle he was driving was “clipped” by another one,
How can a satellite’s speed decrease without its angular momentum changing?
Why do divers executing midair somersaults pull their legs in against their bodies?
It is possible for a body to be both spinning and moving in a circle in such a way that its total angular momentum is zero. Describe how this can be.
Five identical boxes with the same speeds slide along a frictionless horizontal surface. The mass of each box is 10 kg. The same magnitude force, F, is applied to each box, but along different
Eight cars move along smooth horizontal roadways in the same direction at specified speeds, v, toward identical barriers. All the cars have the same size and shape, but carry different loads and,
A 1,000-W motor powers a hoist used to lift cars at a service station.(a) How much time would it take to raise a 1,500-kg car 2 m?(b) If the original motor is replaced with one rated at 2,000 W, how
Six blocks with different masses, m, each start from rest at the top of smooth, frictionless inclines having length d and vertical height h and slide down. Rank the order, from greatest to smallest,
An elevator is able to raise 1,000 kg to a height of 40 m in 15 s.(a) How much work does the elevator do?(b) What is the elevator’s power output?
A compact car can climb a hill in 10 s. The top of the hill is 30 m higher than the bottom, and the car’s mass is 1,000 kg. What is the power output of the car?
It takes 100 minutes for a middle-aged physics professor to ride his bicycle up the road to Alpe d’Huez in France. The vertical height of the climb is 1,120 m, and the combined mass of the rider
When exactly 1 cup of sugar is dissolved in exactly 1 cup of water, less than 2 cups of solution result. Why?
The following terms were introduced: elements, atoms, electrons, protons, neutrons, nucleus, molecules, compounds, mixtures, and solutions.Create a concept map explaining the composition of matter by
Describe the four phases of matter. Compare their external, observable properties. Compare the nature of the forces between atoms or molecules (or both) in the solid, liquid, and gas phases.
Identify some of the elements that exist in pure form (not in compounds) around you.
What would be the mass density, weight density, and specific gravity of aluminum on the Moon? The acceleration of gravity there is 1.6 m/s2.
In Figure 1.13, assume that v1 = 8 m/s and v2 = 6 m/s. Use a ruler to estimate the magnitudes of the resultant velocities in (c) and (d).
Scenes in films or television programs sometimes show people jumping off moving trains and having unpleasant encounters with the ground. If someone is on a moving flatbed train car and wishes to jump
Draw an accurate graph showing distance versus time for the car in Problem 13. What is the slope of the graph?Data from in problem 13How far does a car going 25 m/s travel in 5 s? How far would a jet
During a NASCAR race, a car goes 50 m/s around a curved section of track that has a radius of 250 m. What is the car’s acceleration?
Eight arrows are successively shot straight up into the air. All the arrows have the same size and shape, but are made of different materials and so have different masses (M). The arrows also have
A bungee jumper falls for 1.3 s before the bungee cord begins to stretch. Until the jumper has bounced back up to this height, the elastic cord causes the jumper to have an average acceleration
What is force? Identify several of the forces that are acting on or around you right now.
What is weight? Under what circumstances might something be weightless?
Name the two types of friction. Can both types act on the same object at the same time? If so, give an example of such a circumstance.
A person places a hand on a closed book resting on a table and then presses downward while pushing forward. Either the book slides across the table or the hand slides across the book. What determines
What does a physicist mean by “external” force? In light of Newton’s third law of motion, why can’t an internal force alone produce an acceleration of a system?
At one moment in a football game, player A exerts a force to the east on player B. At the same time, a teammate of A exerts the same-sized force to the south on player B. In what direction is B
Two astronauts in an orbiting space station “play catch” (throw a ball back and forth to each other). Compared to playing catch on Earth, what effect, if any, does the “weightless”
How does an object move when it is subject to a steady centripetal force? How does it move if that force suddenly disappears?
An “extreme” roller coaster is moving along its track. During a brief period the track exerts a downward force on the cars. Describe what is happening. (What is the shape of the trackat this
A single-engine airplane usually has its propeller in the front. Ocean freighters usually have their propeller(s) in the rear. From the perspective of Newton’s second law of motion, is this
As a rocket ascends, its acceleration increases even if the net force on it stays constant. Why?
What is the international system of units (SI)?
An archer aims an arrow precisely horizontally over a large, flat field and lets it fly. At the same instant, the archer’s watchband breaks and the watch falls to the ground. Does the watch hit the
Describe the variation of the net force on and the acceleration of a mass on a spring as it executes simple harmonic motion.
If a 0.5-kg object hanging from a spring stretches it by 0.30m, then by how much will the spring be stretched if a 1-kg object is suspended from it?
Explain how the change in the force of air resistance on a falling body causes it to eventually reach a terminal speed.
The terminal speed of a ping-pong ball is about 20 mph. From the top of a tall building on a windless day, a ping-pong ball is thrown downward with an initial speed of 50 mph. Describe what happens
At least two forces are acting on you right now. What are these forces? Describe the relationship between the size and direction of these two forces.
As any car travels with constant velocity on a straight, flat section of highway, the road still exerts both a vertical (upward or downward) force and a horizontal (forward or backward) force on the
How is Newton’s third law of motion involved when you jump straight upward?
Jane and John are both on roller skates and facing each other. First Jane pushes John with her hands and they move apart. They get together again, and John pushes Jane equally hard with his hands and
People and machines around us do work all the time. But is it possible for things such as magnets and Earth to do work? Explain.
We considered the collision of a karate expert’s hand with a concrete block. Based on the graphs in Figure 1.31, the initial downward speed of the fist with mass 0.75 kg is about −13 m/s and the
Two persons on ice skates stand face to face and then push each other away (Figure 3.45). Their masses are 60 and 90 kg. Find the ratio of their speeds immediately afterward. Which person has the
When climbing a flight of stairs, do you do work on the stairs? Do the stairs do work on you?
A series of five 0.1-kg spheres are arrayed along a thin, lightweight rigid rod with length 0.5 m at intervals of 0.1 m from one end of the rod. The system spins about an axis perpendicular to and
During a head-on collision between two automobiles, the occupants are decelerated rapidly. Use the idea of impulse to explain why an air bag that quickly inflates in front of an occupant reduces the
The graphs in Figure 2.52 show plots of force versus acceleration for several objects. Rank these displays using the identifying numbers according to the mass of the affected object from smallest to
A mass m is attached to a spring with spring constant k, as shown in Figure 2.53. The mass is pulled to the right a distance of 0.2 m and released. Rank the following spring– mass combinations
We computed the force needed to accelerate a 1,000-kg car from 0 to 27 m/s in 10 s. Compute the force using the alternate form of Newton’s second law. The change in momentum is the car’s momentum
Six identical cars are towing identical trailers at constant, albeit different, speeds along level roads in the desert. The trailers carry different loads, so their masses vary. The circumstances of
We have studied four different laws authored by Sir Isaac Newton. For each of the following, indicate which law is best for the task described.(a) Calculating the net force on a car as it slows
In the broadest terms, what causes tides?
The first “Lunar Olympics” is to be held on the Moon inside a huge dome. Of the usual Olympic events—track and field, swimming, gymnastics, and so on—which would be drastically affected by
If suddenly the value of G, the gravitational constant, increased to a billion times its actual value, give several examples of the kinds of things that would happen.
Imagine that two identical containers, one filled with marbles and the other filled with Styrofoam beads, are released simultaneously from rest from the same height—say, 3 m—above Earth’s
Describe how the magnitude of the gravitational force between objects was first measured.
A toaster operating on 120 V uses a current of 9 A.(a) What is the toaster’s power consumption?(b) How much energy does it use in 1 min?(c) What is the total resistance of the heating element wires?
Concept maps can be used as substitutes for traditional note taking when you read articles in magazines and newspapers. This question illustrates the point. Chapter 7 describes a number of
A child on a swing has a speed of 7.7 m/s at the low point of the arc (Figure 3.46). How high will the swing be at the high point? 7.7 m/s
The properties of the top quark have been confirmed with the 2007 discovery of mesons composed of a t quark and a b̅ quark. What charge does such a particle carry? What is its spin? How many units
Analyze the following reactions in terms of their constituent quarks:(a) π+ + p → ∑+ + K+(b) y + n → π- + p(c) p + p → p + p + p + p-(d) K- + p → K+ + K0 + Ω-
The D- meson is a charmed particle with charge -1, charm -1, and strangeness 0. Work out the quark combination for this species of elementary particle.
Give all the quark-antiquark pairs that result in mesons that have no charge, no strangeness, no charm, and no bottomness. How do you think such particles might be distinguished from one another?
What is the quark combination corresponding to an antineutron? An antiproton?
A compact neutron star has a mass of 2.8 x 1030 kg (about 1.4 times the mass of the Sun) but a radius of only 104 m (approximately 6.2 mi!). If a clock on the surface of this exotic star marks the
If a galaxy is found to have a recessional speed of 140,000 km/s, about how far away is it? The current estimate of the precision of the Hubble parameter is approximately 65%. Determine the range
Spectral measurements of a distant galaxy show it to have a redshift z = 0.2. If the wavelength of an ionized calcium line emitted by the galaxy is 393.3 nm, what is the wavelength of this line as
If a proton and an antiproton, both at rest, were to completely annihilate each other, how much energy would be liberated?
A particle of rest energy 140 MeV moves at a sufficiently high speed that its total relativistic energy is 280 MeV. How fast is it traveling?
If a 1.0-kg mass is completely converted into energy, how much energy, in joules, would be released? Compare this value to the amount of energy released when 1.0 kg of liquid water at 0oC
Calculate the rest energy of a proton in joules and MeVs. What is the mass of a proton in MeV/c2?
The formula for length contraction gives the length of an interval on a ruler moving with velocity v relative to an observer as √1 - v2/c2 times the length of the same interval on a ruler at rest
The lifetime of a free neutron is 886 s. If a neutron moves with a speed of 2.9 x 108 m/s relative to an observer in the lab, what does the observer measure the neutron’s lifetime to be?
The lifetime of a certain type of elementary particle is 2.6 x 10-8 s. If this particle were traveling at 95 percent the speed of light relative to a laboratory observer, what would this
The most abundant isotope of lithium, Li-7, contains three protons and four neutrons and has a mass of 7.01600 u. What is the mass defect for this nucleus in atomic mass units? In kilograms?

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