Motion

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```					Motion
The answer is D.
Average speed is defined as distance
traveled divided by the time required for
the trip.
Speed: v = distance / time
Therefore, an acceptable unit would be
any measure of length over any unit of
time.
Miles/hour, km/hr, and m/s are the most
common units
Motion
The answer is B.

Acceleration is defined as the change in
velocity divided by the time it took to
change the velocity.
Acceleration: a = Δv / Δt
Acceleration tells me how fast an object is
getting faster (or slower)
Motion
The answer is E.

Speed = distance / time
Speed = 240 km / 4 hr
Speed = 60 km/hr
Newton’s Laws
The answer is D.
 Newton’s first law states that an object tends to
retain its current state of motion unless acted on
by a net force.
 This is sometimes referred to as the
Law of Inertia.
 More massive objects have more inertia
because they are better at resisting changes in
motion
 There was not enough friction to move the milk
carton with the paper.
Newton’s Laws
The answer is A.
 Weight is the force that an object experiences
due to gravity.
 Newton’s second law states that force is
proportional to mass and acceleration
F=ma
 The acceleration due to gravity on the moon is
less than that on earth, therefore the object will
have a smaller weight
 People often confuse mass and weight. Notice
that the object had the same mass, or amount of
matter, on both the earth and the moon
Newton’s Laws
The answer is D.
Friction is the force that exists between
contacting objects moving past one
another.
It is caused by interactions between the
objects on a microscopic scale, as in the
diagram below.
Friction on an object is always
opposite the direction of the
object’s motion.
Momentum
The answer is A.

Momentum is defined as the product of
an object’s mass and velocity.
Momentum: p = mass * velocity
The units are typically kg m/s
Since the trucks have the same velocity,
the one with the larger mass has a larger
momentum
Momentum
The answer is A.

p = m * v
v = p / m
v = (12 kg m/s) / (4 kg)
v = 3 m/s
Work
The answer is C.
Work is defined as force times the
distance over which the force acts.
Work: W = F * d
Since there was 2 times as much force
and 2 times as much distance…
W = 2F * 2d
W = 4 * (F * d)
The amount of work she did increased by
a factor of 4
Energy
The answer is E.
 Kinetic energy is the energy due to motion
 Potential energy is stored energy
 The pendulum is at rest at the top of the swing so
it has no kinetic energy, but lots of stored
gravitational potential energy
 At the bottom of its swing,
it has no potential because
the potential energy has
been converted to kinetic
energy (it is moving fast!)
Simple Machines
The answer is D.
 Mechanical advantage roughly tells you how
much a machine multiplies the force you apply.
 MA = output force / input force
 Nothing is free!! The trade-off is that you apply
the small force over a large distance to apply the
large output force over a small distance (think
about a wrench or a ramp)
 The amount of work (W = F * d) remains
relatively constant with any loss due to friction
Heat Transfer
The answers are A then B.

Conduction is the transfer of energy as
particles and molecules collide with each
other, as in they have to touch.
Convection is the bulk movement of
heated or cooled material within a sample,
as in warm air rising and cool air sinking.

Convection currents in
boiling water
conduction
Heat Transfer
The answer is C.

Electromagnetic radiation is emitted by the
sun, some of which encounters the Earth,
adding energy to the matter of the Earth
Radiation is the transfer
of energy by emitting
which is then absorbed
by another object
Phase Changes
The answers are E then B.
A phase change is accompanied by the
absorption or release of energy
A diagram for water with common phase
change terms is provided below.
Waves
The answer is C.
 Wavelength is the distance from crest to crest
or trough to trough, measured in meters.
 Amplitude is the size of the disturbance, from
center to peak or center to trough
 Frequency is how many time the disturbance
occurs per unit time, typically in cycles per
second or Hertz
Waves
The answer is D.

Sound is a mechanical wave, meaning
that it requires a medium, or matter, in
order to propagate (travel)
Electromagnetic waves do not need a
medium to travel. “E-mag” waves from the
sun travel to Earth through the
near-vacuum that is outer space!
Waves
The answer is C.
 Waves travel at a certain speed. Wavelength
and frequency are related to speed.
 Wave speed = frequency * wavelength
 Electromagnetic radiation travels at the speed
of light, c (3 x 108 m/s), and the sun is so far
away that it takes almost 8 minutes to reach the
Earth.
 Mechanical wave speed depends on the matter
it is traveling in. Sound is faster in solids than
liquids and slowest in gases.
Light
The answer is D.

Our eyes interpret the frequency of light as
color.
Because frequency is related to
wavelength by speed, another acceptable
answer could be wavelength! But that was
not one of the choices here.
Light and Color
The answer is D.
 The primary colors of light are red, green and
blue
 Red and green light make yellow
 Blue and red make magenta
 Blue and green make cyan
 R, G and B combine to
make white
 Hence, a primary color and its
complement will create white
 Colors opposite each other
on the wheel here produce white
Electric Charge
The answer is B.
 Charges that are of
similar sign,
negative/negative or
positive/positive, will
repel each other
 Charges of opposite
sign will attract
Electricity
The answer is E.
According to Ohm’s Law, voltage is the
product of current and resistance
Voltage: V = I * R
I is the symbol for current and R is the
symbol for resistance
In this problem…
V=I*R
V = 5 A * 10 ohms
V = 50 Volts
Electricity
The answer is E.

A complete circuit needs a voltage source
(like a battery), wires to connect all of the
components, and a load to consume the
energy (such as a light bulb, or your iPod!)
Electric Circuits
The answer is B.
 For resistors in series,
resistances together to
1      1    1                    determine total resistance
         ...
Rtotal R1 R 2                     For parallel circuits, the
inverse of the total
resistance is equal to the
sum of the inverses of
each resistor (see eqn.)
 This problem was a
series circuit
series                parallel
Rtotal    R1  R2 ...     1        1   1        Rtot = R1 + R2
        ...   Rtot = 3 ohms + 6 ohms
Rtotal R1 R 2
Rtot = 9 ohms

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 views: 15 posted: 11/20/2010 language: English pages: 46