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
 electromagnetic rad.
 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,
                                                  simply add the
                                                  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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