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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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posted: | 11/20/2010 |

language: | English |

pages: | 46 |

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