Physics Exam 2 7/20/20

What is the volume of a sugar cube that measures 1 cm on each side? What is the cross-sectional area of the cube? The total surface area?

1 cm^3, 1 cm^2, 6 cm^2 (opened up)

What is the mass density of water? What is the weight density of water?

1000 kg/m3; 9800 N/m3

Compared to the mass of a hydrogen atom, the mass of an oxygen atom is

16 times as great.

How many protons should be added to the nuclei of oxygen atoms so the resulting gas will glow red when there is an electric current through it?

2

Cube A has a length of 1 cm and cube B has a length of 3 cm. How much more is the volume of cube B, compared to that of cube A?

27 times larger volume is width cubed: 3 cubed=27

If the linear dimensions of an object are doubled, by how much does the surface area increase? By how much does the volume increase?

4 times, 8 times (As the linear size of an object increases, the volume grows faster than the total surface area.)

If a 1-kg object stretches a spring by 2 cm, then how much will the spring be stretched when it supports a 3-kg object? (Assume the spring does not reach its elastic limit.)

6 cm

How many shells are represented in the presently known periodic table?

7

How many atoms are in a molecule of ethanol, C2H6O?

9

Cube A has a length of 1 cm and cube B has a length of 3 cm. How much larger is the surface area of one of the faces of cube B, compared to that of cube A?

9 times larger area is width squared: 3 squared = 9

How do you explain the saying "The bigger they are, the harder they fall" using scaling?

A big creature has a small ratio of surface area to mass, so air resistance doesn't slow it as much when it falls. >>consequence of the small ratio of surface area to weight. Air resistance to movement through the air depends on the surface area of the moving object. *use a parachute!

What is the purpose of a model in science?

A model is an abstraction that helps us visualize and predict.

How does a molecule differ from an atom? Give an example.

A molecule is composed of two or more atoms bonded together: H2O.

What is meant by the term nucleon?

A proton or neutron

Distinguish between tension and compression.

A pulled-apart object is in tension; a pushed-together one is in compression.

Why can small creatures fall considerable distances without injury, while people need parachutes to do the same?

A small creature has greater surface area per unit mass, so air resistance slows it more when it falls.

What is meant by the elastic limit for a particular object?

A spring is elastic up to the limit and inelastic above it.

Who first explained Brownian motion and made a convincing case for the existence of atoms?

Albert Einstein

Why can't atoms be seen with a powerful optical microscope?

Atoms are much smaller than a wavelength of light.

How does the arrangement of atoms in a crystalline substance differ from the arrangement in a noncrystalline (amorphous) substance?

Atoms in crystals are in an ordered array. In amorphous materials, they are randomly distributed.

What is a compound? Cite two examples.

Atoms of different elements with bonds between them: NaCl and H2O

What is a mixture? Cite two examples.

Atoms pressed together without bonding: air and salt and sand

Where were the atoms that make up a newborn infant "manufactured"?

Atoms were "manufactured" in the stars that exploded in the origin of the universe, before the Sun and Earth came into existence. Depending on the weight of the atoms, lighter ones were created deep within stars, while heavier ones were formed in the implosion and explosion of supernovas.

What are the five most common elements in humans?

C, H, O, N, and Ca

What causes dust particles and tiny grains of soot to move with Brownian motion?

Collisions with invisible molecules

Is it tension or compression that strengthens an arch that supports a load?

Compression

What happens to the volume of a loaf of bread that is squeezed? The mass? The density?

Decreases, stays the same, increases

What kind of attraction pulls electrons close to the atomic nucleus?

Electric

The atoms that constitute your body are mostly empty space, and structures such as the chair you're sitting on are composed of atoms that are also mostly empty space. So why don't you fall through the chair?

Electrons in one atom repel the electrons in another atom. The same goes for the positively charged nucleii. Repulsion increases rapidly as the nucleii get closer to each other. Also, solid material molecules are held together by various kinds of bonds. These bonds (chemical) would need to be broken to pass through. This would require a significant amount of energy!

Since atoms are mostly empty space, why don't we fall through a floor we stand on?

Electrons in one atom repel the electrons in another.

Which requires more food daily: an elephant or a mouse? Which requires more food per unit of body weight: an elephant or a mouse?

Elephant, mouse

Which has more skin: an elephant or a mouse? Which has more skin per unit of body weight: an elephant or a mouse?

Elephant, mouse surface area per vol of material (ex. thin fries cook faster than thick!)

You could swallow a capsule of germanium without ill effects. But, if a proton were added to each of the germanium nuclei, you would not want to swallow the capsule. Why?

Germanium, the apparently harmless element, has 32 protons (atomic number 32). Adding a proton to a germanium nuclei would give it properties of a 33 proton element- this happens to be Arsenic! As we know, Arsenic is poisonous.

What is the evidence that dark matter exists?

Gravitational forces within galaxies are too great to be accounted for with ordinary matter.

What element has the lightest atoms?

Hydrogen

Which of the following is an element?

Hydrogen

Where in the atom is most of its mass concentrated? What is this mass composed of?

In the nucleus as protons and neutrons

As a cube gets bigger, how does the ratio of the surface area to volume change?

It decreases.

How does one isotope differ from another?

It has a different number of neutrons.

How does the electric charge of a proton compare with the electric charge of an electron?

It is equal and opposite.

Who advanced the idea of atoms in the early 1800s?

John Dalton

Distinguish between mass number and atomic mass.

Mass number is the number of nucleons; atomic mass is the total mass of an atom.

How would you test the notion that a steel ball is elastic?

Material that returns to its original shape after it has been stretched or compressed is said to be elastic. When the ball is hit, the force will temporarily change the steel ball's shape. A body's elasticity describes how much it changes shape when a deforming force acts on it, and how well it returns to its original shape when the deforming force is removed.

Which of these statements is true?

Molecules are the smallest subdivision of matter that still retains chemical properties of a substance.

Are most of the atoms around us younger or older than the Sun?

Most are older than the Sun.

Which of the following is not a mixture?

None. All of the above choices are mixtures.

Where did the heaviest elements originate?

Nuclear fission in supernovas

How are most of the elements with nuclei heavier than those of hydrogen and helium formed?

Nuclear fusion in stars

Why were so many vertical columns needed to support the roofs of stone buildings in ancient Egypt and Greece?

Stone breaks under tension.

What is Hooke's law? Does it apply to elastic materials or to inelastic materials?

Stretch is proportional to force for elastic materials.

What does the strength of a person's arm usually depend on?

The cross-sectional area

Silicon is the chief ingredient of both glass and semiconductor devices, yet the physical properties of glass are different from those of semiconductor devices. Explain.

The crystalline structure of silicon may be more evident in one than the other. Very pure silicon is used in semiconductor devices. Glass is an amorphous solid (non-crystalline), a compound with many other ingredients.

Iridium is not the heaviest atom found in nature. What, then, accounts for a chunk of pure iridium being the densest substance on Earth?

The iridium atoms are closer together in the crystalline form.

Why aren't heavier elements much larger than lighter elements?

The larger positive charge in the nucleus pulls the electrons into closer orbits.

What and where is the neutral layer in a beam that supports a load?

The layer in which there is neither tension nor compression along the middle from end to end

What does the atomic number of an element tell you about the element?

The number of protons in its nucleus

How does the approximate number of atoms in the air in your lungs compare with the number of breaths of air in Earth's atmosphere?

The numbers are the about the same, 10^23.

Compared with the energy it takes to separate oxygen and hydrogen from water, how much energy is released when they recombine?

The same amount of energy is released when they recombine.

Why isn't cement needed between the stone blocks of an arch that has the shape of an inverted catenary?

The stones are held together by compressive forces.

Why can atoms be seen with an electron beam?

The wavelength of the electrons is smaller than an atom.

Why aren't vertical columns needed to support the middle of domed stadiums, such as the Houston Astrodome?

The weight produces compression that supports the dome.

The uranium atom is the heaviest and most massive atom among the naturally occurring elements. Why, then, isn't a solid bar of uranium the densest metal?

There must be more spacing in between atoms of a uranium sample, giving it a smaller density than that of close-packed, lighter iridium atoms. The density of a material depends upon the masses of the individual atoms that make it up, and the spacing between those atoms. density= mass/vol. The close spacing of iridium atoms in an iridium crystal gives it the greatest density. A cubic centimeter of iridium contains more atoms than a cubic centimeter of gold or uranium.

What occurs when a proton and an antiproton meet?

They annihilate each other.

Why do some animals curl up into a ball when they are cold?

They are decreasing the amount of surface area exposed to the cold, to reduce the amount of body heat lost. The heat that an animal generates is proportional to its mass (or volume), but the heat that it can dissipate is proportional to its surface area.

Which is denser: an object that has a density of 1000 kg/m3 or one that has a density of 1 g/cm3?

They are the same density!

Why are the cross-sections of metal beams in the shape of the letter I instead of solid rectangles?

To reduce the weight of the beam while preserving the resistance to bending

Why do we say that a blob of putty is inelastic?

When deformed, it does not return to its original shape.

Why do we say that a spring is elastic?

When deformed, it returns to its original shape.

How do matter and antimatter react to each other?

When matter and antimatter meet, they annihilate in a flash of energy.

Can a horizontal I-beam support a greater load when the web is horizontal or when the web is vertical? Explain.

When the web of an I beam is horizontal (shaped H) the top and bottom flanges are not bearing the weight as much; the web will be bearing the load (since the flanges will be vertical!) This will not be as strong. When the web of an I beam is vertical (shaped I), the top and bottom flanges are bearing the weight. The flanges will also be flat horizontally. consider bending a ruler one way (long) and another (width)

Somebody told your friend that if an antimatter alien ever set foot upon Earth, the whole world would explode into pure radiant energy. Your friend looks to you for verification or refutation of this claim. What do you say?

While the meeting of antimatter and matter would result in a transformation of radiant energy, the amount of matter reacting would only equal the amount of antimatter reacting. Thus, if the antimatter alien set foot on Earth, only an amount of Earth equal to the alien's mass would react and explode.

What evidence can you cite for the microscopic crystal nature of certain solids? For the macroscopic crystal nature?

X-ray diffraction and the macroscopic shape of crystals

What is the advantage to a gymnast of being short in stature?

a lower center of gravity. This means that the gymnast can balance more readily than her taller peers.

The smallest particle of those listed below is

a quark.

Nuclei of atoms that make up a newborn baby were made in

ancient stars.

The atomic masses of two isotopes of cobalt are 59 and 60. What is the number of protons in each? What is the number of neutrons in each? What is the number of orbiting electrons in each when the isotopes are electrically neutral?

cobalt-59, cobalt-60 = 27 protons each. Isotopes still have the same atomic number. 32 neutrons,33 neutrons. Subtract the protons from the isotope number to find the specific number of neutrons. (p+n=isotope#) 27 electrons each (matches proton #, which is again same for each)

A force that determines the chemical properties of an atom is a(n)

electrical force.

The volume of matter comes mostly from its

electrons

To become a negative ion, does an atom lose or gain an electron?

gains

When carbon and oxygen atoms combine, energy is

given off by the reaction.

If one neutron is added to a helium nucleus, the result is

helium.

Which has the greatest number of protons in its nucleus?

lead.

To become a positive ion, does an atom lose or gain an electron?

loses

The reason a granite block is mostly empty space is that the atoms in the granite are

mostly empty space themselves.

Which of the following are electrically neutral?

neutron

Solid matter is mostly empty space. The reason solids don't fall through one another is because

of electrical forces.

Your friend says that what makes one element distinct from another is the number of electrons about the atomic nucleus. Do you agree wholeheartedly, partially, or not at all? Explain.

partially. Another characteristic and distinguishes elements is the number of protons in one's nucleus (the atomic number)

Dark matter is considered to be _______.

plentiful in the universe

The weight of matter comes mostly from its

protons and neutrons.

Brownian motion has to do with the

random motions of atoms and molecules.

In our part of the universe, antimatter is

short-lived.

If we doubled the magnifying power of the most powerful optical microscope in the world, we would

still not be able to see or photograph an atom.

Compared to the atoms that make up the body of an elderly person, the atoms that make up the body of a newborn baby are

the same age.

There are about as many atoms of air in our lungs at any moment as there are breaths of air in the atmosphere of

the whole world.

Atoms heavier than helium were made by

thermonuclear fusion.

The number of atoms in a common water molecule is _______.

three

How many different elements are in a water molecule?

two

Which of these atoms has the greatest amount of electrical charge in its nucleus?

uranium

Which of these atoms has the greatest number of electrons?

uranium

Which of these atoms has the most mass?

uranium