Physics 115 Future Physics
Midterm Review
2015
Exam will be closed book; no calculators; no computers.
You can bring a 3 x 5 index card with whatever notes and equations
you want written on ONE SIDE ONLY. You will sign the other side
and turn it in with your exam.
In addition to review session, there will be a help session on Tuesday
in class (October 27).
In addition to answering these questions, check them against the
Learning Goals to make sure they cover the material and there are
no gaps in your preparation.
Energy and Power
How is energy related to heat? What is heat?
What is an explosion?
What is energy? What is power? How do they differ? What are the units used to describe both?
What are the quantitative relations between Calories, joules, kilojoules? How many bites of a
chocolate bar contains a Calorie of energy? A kilojoule of energy?
What is the quantitative relation between kilowatts and horsepower? What do they measure?
When you walk to class, about how many horsepower (and kilowatts) do you use? As a 21st
century student in the US, about how much total power do you consume both directly and
indirectly?
Energy game: How does the energy per gram of TNT compare to a cookie? Why do we use TNT
instead of cookies to blow up things? How do these compare to uranium, etc.? Why isn’t uranium
explosive? What forms of energy do each have?
What is mass and what are its units? How many kg is 100 lbs?
What is the equation E=mc2 telling us about mass and energy?
Check if the units agree on both sides of this equation.
What do bullets and asteroids have in common? Why do their energies per gram differ by a factor of
100,000? What does this number tell you about their relative speeds? Can you calculate the relative
speeds? If the bullet is moving at the speed of sound, how fast is the asteroid moving?
Why is hydrogen a potential fuel? How does it work? What are its advantages and
disadvantages? Why is this an example where it costs energy to make energy? Why aren’t we
using hydrogen instead of gasoline already?
What is kinetic energy? What is the formula? The units? How does the kinetic energy change if you
double the mass? The speed?
Same questions for momentum.
What is conservation of energy? Conservation of momentum? Find an example where conservation
of energy is the easiest (only?) way to solve a problem. Find an example where conservation of
momentum is the only way to solve a problem.
Which equations that we use are “1” equation and which are “3 in 1”?
If a bomb explodes and breaks into two pieces in which one is twice the mass of the other, what can
you say about the directions the two pieces travel? Their speeds? Their kinetic energies? Which piece
would cause more damage if it hit you? Explain why.
Why does a block of uranium have so much more energy than a fastball? What form of energy is it?
(nuclear energy is not good enough: I mean microscopically, what kind of energy is being converted
into heat?)
Atoms and Heat
Why do a plastic and glass cup at the same temperature feel as if they are at different temperatures
when you touch them? Why do copper and iron heat up at different rates even when placed under
the same flame?
What is heat? How is heat related to temperature? What is specific heat and what does it depend on?
What is room temperature in degrees Centigrade? Kelvin? Fahrenheit?
If a substance has high specific heat, does it mean that it conducts heat easily? Or it doesn’t? Or you
cannot tell just by known the specific heat? Explain.
If I double the mass and triple the temperature of an object, by what factor have I changed the heat
energy?
If the object began at room temperature, what is temperature after you have tripled it?
Do two objects at the same temperature and with the same mass have the same amount of heat
energy? Explain why or why not? If not, given examples where it is not so.
What are the four laws of thermodynamics?
If you mix two cups of water at different temperatures, what temperature will they reach over time?
How does it depend on the temperature and volume of water in the two cups?
Is the specific heat of water greater or less than aluminum, and what does that information tell us?
How is temperature related to the physical properties of atoms: How does it depend on their mass and
speed?
What is the typical speed of atoms and molecules in materials?
Gold has about 7 times the atomic mass as aluminum and about 1/7th the specific heat. If a kg mass of
gold and a kg mass of copper at the same temperature, which of the following are the same? And if
different, why and by what factor?: (1) heat energy; (2) kinetic energy per atom; (3) speed per atom.
What is the size of an atom? (compare to something you know, like the width of a hair)
In a sealed can, how is pressure related to temperature in a gas? How is this related to explosions?
How does the kinetic energy of a fastball when thrown by a pitcher compare to its heat energy at rest?
A ssum e the throw n ball w as very cold before it w as throw n. Be quantitative.
How can you use this to estimate the temperature the shuttle reaches when it enters and slows down
in the atmosphere?
When you heat water, does it expand or contract? By about what factor? When you melt ice, does it
expand or contract?
If a 1 m steel ruler is heated by 100 degrees C, by how much (in meters) does it expand?
Which is easier: converting kinetic energy to heat or converting heat to kinetic energy? Or is it
equally easy? What laws of thermodynamics apply? What has this to do with order and disorder?
What is entropy?
What is a heat engine? How do we compute the ideal (maximally possible) efficiency of a
heat engine?
Force and Gravity
What is force? What are it units? What is acceleration? What are its units? How does force depend
on mass and acceleration? What is the relation between the direction of the force and the direction of
the acceleration? the direction of the velocity?
Can you name an example in which the net force and acceleration are in opposite directions? Can
you name an example in which the net force and velocity are in opposite directions? Can you give
an example in which the net force and acceleration are at right angles? Can you give an example in
which the net force and velocity are at right angles?
What does the law of action-reaction mean? Why don’t forces always cancel because of it? How is
the law related to conservation of momentum?
What are Newton’s three laws?
Name three conservation laws obeyed by any closed system.
What is the expression for the gravitational force and potential energy near the surface of the
Earth? Check the units in your expression to see if they make sense.
When you throw an object at an angle near the surface of the Earth, name 2 quantities that remain
constant throughout its motion. Name 3 quantities that change continuously.
Why does circular motion at constant speed require a force? Which remains constant during circular
motion: the velocity? the speed? the acceleration? the force? the momentum? the kinetic energy? For
those that change, how do they change?
How high above the Earth’s surface do you have to go to feel weightless? Give examples of
how you can experience weightlessness.
How is orbiting related to falling? to weightlessness? How does the direction and magnitude
of the gravitational force change an object is orbiting?
If you throw an apple in the air as you jump off a diving board, which will hit the ground first? If
two divers walk off the end of a diving board at different speeds, which one hits the water first?
If one diver let’s go of a ball on the way down, what happens to the motion of the ball relative to
the diver? Explain.
If an object travels at a constant velocity (speed and direction), what can you conclude about the NET
force on the object? If a car turns a corner at constant speed, what can you conclude about the NET
force during the turn? Can you say something about its direction?
If you are driving a car in a straight line at constant speed, what is the net force on your car? Given
you answer, why do you need to use your engine at all?
Explain how you compute the terminal velocity of an object dropped in air. What does the terminal
velocity depend on?
Why is it easier to land a rocket on the moon than to predict the weather a week from now?
How does air resistance affect gas consumption? Use this explain whether it costs more gas to travel
30 mph or 60 mph if you want to travel from Princeton to New York City.
Radioactivity and Radiation
What is radioactivity? How is it different from radiation?
What information would you need to calculate how much energy (in calories) is released in the
radioactive decay of a single nucleus?
In a radioactive decay such as alpha or beta decay, which is more dangerous, the resulting nucleus or
the lighter (alpha or beta) particles? Be prepared to explain why using the conservation of
momentum and energy.
What is an alpha ray? Beta ray? Gamma ray?
Which type of ray is easiest to stop? Which is hardest to stop?
To have a radioactive decay, what condition(s) have to be satisfied about the nucleus that decays and
the nuclei and rays that are produced from the decay?
Name four conservation laws that apply to radioactive decays.
What does atomic mass tell us about the nucleus? What does atomic number tell us?
What is an isotope? If two atoms have nuclei that are different isotopes of the same element, how
does this affect their chemical properties? Nuclear properties?
How much radiation exposure is typical in a year? Hazardous? Lethal?
How do you use the “linear hypothesis” to estimate the risk of cancer to a person for a given
exposure? The number of cancers in a population?
What is a chain reaction? Explain in detail how neutrons play a role and what condition needs
to be satisfied to have a runaway chain reaction.