Physics - Final Exam Review
Discuss the differences between an elastic and inelastic collision--which collision conserves KE?
elastic - objects remain stuck together & KE is conserved inelastic - objects separate & KE is not conserved
What does it mean when someone says charge is polarized?
electrons move inside the object so one side is positive and the other is negative
AC is delivered to your home with what voltage?
120 V
How much more momentum will a car have when it increases its speed from 40 mph to 80 mph?
2 times more momentum
AC is delivered to your home with what frequency?
60 Hertz
In the equation F = ma, how are F and m related? F and a? m and a?
F & m - directly; F & a - directly; m & a - inversely
What is the SI unit for charge?
Coulombs (C)
Does a battery produce AC or DC?
DC current
explain the difference between PEg and KE
PEg - (stationary objects) occurs when an object is lifted above some reference point; energy stored when an object gains height KE - (moving objects) the energy associated with objects that are moving
compare and contrast PEg and PEe
PEg - the potential energy associated with gravitational force PEe - the potential energy of an elastic object that is deformed under tension or compression
A car travels at a constant speed "v" up a hill from point A to point B, as shown in the diagram below. As the car travels from A to B, its gravitational potential energy does what? What happens to its KE?
PEg increases, KE stays the same
What is the approximate resistance of the human body when dry? When wet?
dry- 100,000 ohms | wet- 1,000 ohms
Hector says that adding bulbs in series to a circuit provides more obstacles to the flow of charge, reducing current in the circuit. Jeremy says that adding bulbs in parallel provides more paths so more current can flow. With whom do you agree or disagree?
agree with both
Air bags save thousands of lives a year. How does an airbag save lives where "bare" steering wheels often severely injure or kill people?
air bags increase the time of collision and decrease the force of impact
conductor
allow electricity to flow, high conductivity, low resistivity
What is a capacitor?
an electrical component that is easy to change and from which the electrical energy it stores is easy to retrieve
An unfortunate bug splatters against the windshield of a moving car. Describe the forces, impulses, momentum changes, and accelerations of both the bug and the car?
bug and car experiences the same force; the bug experiences the greater impulse, momentum change, and acceleration change
What is the unit for current, resistance, voltage, and power?
current- Amp (A) | resistance- Ohm | voltage- Volts (V) | power- Watts (W)
What device is used to measure current and voltage in a circuit? How do you insert each into circuit -in series or parallel?
current- ammeter | voltage- voltmeter | ammeter- series | voltmeter- parallel
A small, positively charged object near a negatively charged sphere is moved closer to the sphere. The electrical potential energy of the small object will increase or decrease?
decrease
What does an electroscope do?
detects whether an object is charged and indicates whether it's positive or negative
Do an ampere and a volt measure the same thing, or different things? What are those things, and which is a flow and which is the cause of the flow?
different; ampere- current | volt- potential drop | current is the flow and volt causes the flow
How are momentum and impulse related?
impulse is the change in momentum
A small, positively charged object near a positively charged sphere is moved closer to the sphere. The electrical potential energy of the small object will increase or decrease?
increase
A car's speed doubles and the mass triples, by what factor will the KE change?
increase by a factor of 12
The speed of a car is doubled—by what factor is its momentum changed?
increase by a factor of 2
A car's speed doubles, by what factor will the KE change?
increase by a factor of 4
If the speed of a moving object is doubled, the kinetic energy of the object will increase or decrease by what factor?
increase by a factor of 4
The speed of a car is doubled—by what factor is its kinetic energy changed?
increase by a factor of 4
If the charge of one particle doubled and the charge of the other particle tripled, by what factor would the electrostatic force between the particles change?
increase by a factor of 6
If the charge of one particle were reduced to one- half the original charge and the distance between the charges were multiplied by 2, by what factor would the electrostatic force between the particles change?
increase by a factor of 8
A positive charge and a negative charge held near each other are released. As they move, the force on each particle increases or decreases?
increases
When the distance between two charges is halved, how the electrical force between the charge?
increases by a factor of 4
Why did AC win the AC/DC war?
it can be transformed to higher/lower voltages
In terms of momentum change, explain why it is best to "give" when catching a baseball. Provide other examples of situations in which you want to lengthen the impact time in a collision.
it decreases the force by increasing the time of impact; egg toss is another example
What role does a resistor play in a circuit?
it reduces the current flow; built to provide a measured amount of "resistance" to electrical flow and reduce the current
If the charge of each particle tripled and the distance also tripled, by what factor would the electrostatic force between the particles change?
it stays the same
What four things does resistance depend on?
length, thickness, diameter, temperature
discuss the simple machines--list examples of each type.
lever - a simple machine made of a bar that turs about a fixed point pulley - changes the direction of a force; a grooved wheel with a rope or chain
What types of charges repel? Which one's attract?
like charges repel; opposite charges attract
semi-conductor
material that has conductivity between a conductor and an insulator
What is momentum and impulse?
momentum - a measure of how hard it is to stop or turn a moving object impulse - the product of an external force and time which results in a change in momentum of a particle or system
Two charged particles held close to each other are released. As they move, the force on each increases. Therefore, the particles have the same or different sign?
opposite signs
If the charge of one particle were reduced to one- half the original charge and the distance between the charges were multiplied by 2, how would the |electrostatic force between the particles change?
reduced by a factor of 8
Two charges are separated by a certain distance. If the magnitude of each charge is tripled, how will the force on each charge change according to Coulomb's Law?
reduced by a factor of 9
What happens to the overall resistance in a circuit when light bulbs are added in parallel? lf one goes out will they all go out?
resistance decreases; others will remain lit
What happens to the overall resistance in a circuit when light bulbs are added in series? If one goes out will they all go out?
resistance increases; if one goes, they all go
insulators
resists the flow of electricity, low conductivity, high resistivity
Discuss the naked egg drops--why did some students' eggs break while others did not?
some suffered a greater impulse; some experienced greater force than others or less time of impact
A boy fires a table tennis launcher. Briefly describe the forces and impulses on the launcher and the ball--which has more momentum? which is moving faster?
the ball has more momentum, moves faster, and has a greater impulse; they experience the same force
Why are modern automobiles designed to "crush" around their passengers?
the crumple zone increases the time of the collision and decreases the force of the collision
What is electric potential energy? What is the unit for PEelectric?
the energy due to the position of a charge near other charges; joules (J)
What is mechanical energy?
the energy due to the position of something or the movement of something
Mr. Laney is driving down the road at a velocity of 80 mph east when his car brakes go out! Up ahead, Laney sees two options: he can run into a brick wall or a pile of hay--which should he choose?
the pile of hay--his stopping time will increase, decreasing his force of impact
Explain how to charge something by induction.
the process of charging objects without direct contact (through a charged object and something else)—grounding is an example
Which has more momentum--a rabbit running at 5 mph or a 1500 kg Ram truck at rest?
the rabbit--the truck has no momentum if it's at rest
What is electric potential? What is the unit for electric potential? What is the equation for electric potential?
the ratio of electric potential energy to charge; units- Volts; eq: V = IR or V = kq/r
What is efficiency?
the ratio of the useful output to the total energy input of the system. eff = F out/F in or d out/d in
Two lamps, one with a thick filament and one with a thin filament, are connected in series to a battery. Which lamp has the greater current?
the thick one has less resistance
Two lamps, one with a thick filament and one with a thin filament, are connected in series to a battery. Which lamp has the greater voltage drop?
the thin one has more resistance & more voltage drop
Explain how to charge something by friction
the transfer of elections through touch; friction -> when electrons are transferred by a friction from one object to another
You do work when you lift it against gravity. How does this work relate to gravitational potential energy? If the lifted object is released, what becomes of this energy?
the work done lifting the box is stored as PEg,; if the box is dropped, PEg is turned into KE
A mountain climber increases his height by a factor of 3. What happens to the climber's PE?
their potential energy increases by a factor of 3
Two people who weigh the same amount climb a flight of stairs. The first person climbs the stairs in 30 s while the second person climbs them in 40 s. Which person does more work? Which uses more power?
they both do the same amount of work, but the first person uses more power
A large truck and a little itty bitty Ford Focus have a head-on collision--which vehicle experiences the greatest force of impact? which vehicle experiences the greatest impulse? which vehicle experiences the greatest momentum change?
they experience the same force; the Ford Focus has a greater impulse and momentum change
Mr. Laney shoots a shotgun. Discuss the forces and accelerations in both the gun and bullet--which one experiences the greater force? the greater acceleration?
they experience the same force; the bullet experiences greater acceleration
Two lamps, one with a thick filament and one with a thin filament, are connected in parallel to a battery. Which lamp has the greater current?
thick filament = less resistance = more current
Will resistance be higher in a thin wire or a think wire?
thin wire
Two lamps, one with a thick filament and one with a thin filament, are connected in parallel to a battery. Which lamp has the greater voltage drop?
voltage is constant in parallel
superconductor
zero electrical resistivity
