# Conceptual physics chapter 9 assess answers

## Presentation on theme: "Conceptual Physics Chapter 9: ENERGY."— Presentation transcript:

1 Conceptual Physics Chapter 9: ENERGY 2 This lecture will help you understand:Energy Work Power Mechanical Energy : Potential and also Kinetic Work-Energy Theorem Conservation of Energy Machines Efficiency Recycled Energy Energy for Life Sources of Energy 3 Energy A combicountry of energy and also issue comprise the cosmos.

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EnergyMover of substances Both a thing and a process Observed as soon as it is being moved or being transformed A conserved amount 4 Energy Matter Property of a device that allows it to perform workAnypoint that can be turned right into warmth Example: Electromagnetic waves from the Sun Matter Substance we deserve to see, smell, and feel Occupies room 5 Work Work Two points happen whenever before occupational is done:involves force and also distance. is force  distance. in equation form: W  Fd. Two points happen whenever before work-related is done: application of pressure movement of somepoint by that force 6 Work CHECK YOUR NEIGHBORIf you push against a stationary brick wall for several minutes, you do no occupational A.on the wall. at all. Both of the above. None of the over. A. on the wall. 7 Work CHECK YOUR ANSWER If you push versus a stationary brick wall for numerous minutes, you carry out no work-related A.on the wall. at all. Both of the over. None of the above. Explanation: You might do job-related on your muscles, but not on the wall. A. on the wall. 8 Work Examples: Twice as much occupational is done in lifting 2 lots 1 story high versus lifting 1 pack the exact same vertical distance. Reason: force essential to lift twice the load is twice as much. Twice as a lot occupational is done in lifting a load 2 stories rather of 1 story. Reason: distance is twice as great. 9 Work Example: Unit of work: newton-meter (Nm)a weightlifter increasing a barbell from the floor does work-related on the barbell. Unit of work: newton-meter (Nm) or joule (J) 10 Work CHECK YOUR NEIGHBORWork is done in lifting a barbell. How much job-related is done in lifting a barbell that is twice as heavy the exact same distance? A.Twice as a lot Half as a lot The same Depends on the speed of the lift A. Twice as much. 11 Depends on the rate of the liftWork CHECK YOUR ANSWER Work is done in lifting a barbell. How a lot occupational is done in lifting a barbell that is twice as heavy the same distance? A.Twice as a lot Half as a lot The exact same Depends on the speed of the lift Explanation: This is in accord via job-related  force  distance. Twice the force for the exact same distance means twice the job-related done on the barbell. A. Twice as a lot. 12 Work CHECK YOUR NEIGHBORYou perform job-related when pushing a cart through a constant pressure. If you push the cart twice as far, then the work you do is A.less than twice as much. twice as a lot. more than twice as much. zero. B. twice as a lot. 13 A. less than twice as much. twice as a lot. even more than twice as much. Work CHECK YOUR ANSWER You carry out work when pushing a cart through a constant pressure. If you push the cart twice as much, then the job-related you perform is A.less than twice as a lot. twice as much. more than twice as much. zero. B. twice as much. 14 Power Power: Measure of exactly how fast job-related is done In equation form: 15 Power Example: A worker uses even more power running up the stairs than climbing the same stairs gradually. Twice the power of an engine deserve to perform twice the work-related of one engine in the very same amount of time, or twice the work-related of one engine in fifty percent the moment or at a price at which energy is adjusted from one form to one more. 16 Power Unit of power joule per second, called the watt after James Watt, developer of the heavy steam engine 1 joule/second  1 watt 1 kilowatt  1000 watts 17 Power CHECK YOUR NEIGHBORA task can be done progressively or conveniently. Both may call for the exact same amount of work, however various quantities of A.power. momentum. power. impulse. C. power. 18 Power CHECK YOUR ANSWERA project can be done slowly or easily. Both may call for the exact same amount of work-related, but different amounts of A.energy. momentum. power. impulse. Comment: Power is the rate at which work is done. C. power. 19 Mechanical Energy Mechanical energy is because of position or to activity, or both. Tbelow are two forms of mechanical energy: Potential power Kinetic energy 20 Potential Energy Example:Stored energy organized in readiness through a potential for doing occupational Example: A extended bow has actually stored power that have the right to do work-related on an arrowhead. A extended rubber band also of a slingswarm has actually stored energy and also is qualified of doing work. 21 Potential Energy—GravitationalPotential energy due to elevated position Example: water in an elevated reservoir elevated ram of a pile driver 22 Potential Energy—GravitationalEqual to the job-related done (force required to relocate it upward  the vertical distance relocated against gravity) in lifting it In equation form: Potential energy  mass  acceleration because of gravity  height  mgh 23 Potential Energy CHECK YOUR NEIGHBORDoes a vehicle hoisted for repairs in a service station have increased potential energy family member to the floor? A.Yes No Sometimes Not enough information A. Yes. 24 Potential Energy CHECK YOUR ANSWERDoes a auto hoisted for repairs in a organization station have increased potential energy family member to the floor? A.Yes No Sometimes Not sufficient indevelopment Comment: If the car were twice as hefty, its boost in potential energy would be twice as good. A. Yes. 25 Potential Energy Example: Potential power of 10-N ball is the very same in all 3 situations because work done in elevating it is the same. 26 Kinetic Energy Energy of motionDepends on the mass of the object and square of its speed Include the proportional continuous 1/2 and also kinetic power  1/2  mass  speed  speed If object speed is doubled  kinetic energy is quadrupled. 27 Must a automobile through momentum have actually kinetic energy?CHECK YOUR NEIGHBOR Must a auto through momentum have actually kinetic energy? A.Yes, as a result of motion alone Yes, once activity is nonincreased Yes, because speed is a scalar and also velocity is a vector quantity No A. Yes, due to movement alone. 28 Must a vehicle through momentum have kinetic energy?CHECK YOUR ANSWER Must a car with momentum have kinetic energy? A.Yes, because of activity alone Yes, once momentum is nonincreased Yes, because speed is a scalar and also velocity is a vector amount No Explanation: Acceleration, rate being a scalar, and also velocity being a vector amount are irpertinent. Any relocating object has actually both momentum and kinetic energy. A. Yes, as a result of movement alone. 29 Kinetic Energy Kinetic energy and also occupational of a moving objectEqual to the job-related compelled to carry it from rest to that speed, or the work the object can execute while being brought to remainder In equation form: net pressure  distance  kinetic energy, or Fd  1/2 mv2 30 Work-Energy Theorem Work-energy theoremGain or reduction of energy is the result of work. In equation form: occupational  readjust in kinetic energy (W  KE). Doubling speed of a things needs 4 times the job-related. 31 Work-Energy Theorem Applies to decreasing speed:reducing the rate of a things or bringing it to a halt Example: Applying the brakes to slow a relocating vehicle, occupational is done on it (the friction force provided by the brakes  distance). 32 A. F  ma. B. Ft  mv. C. KE  1/2mv2. D. Fd  1/2mv2.Work-Energy Theorem CHECK YOUR NEIGHBOR Consider a trouble that asks for the distance of a fast-relocating crate sliding throughout a factory floor and then coming to a soptimal. The most useful equation for resolving this trouble is A. F  ma. B. Ft  mv. C.KE  1/2mv2.

D.Fd  1/2mv2. D. Fd = 1/2mv2. 33 Work-Energy Theorem CHECK YOUR ANSWERConsider a difficulty that asks for the distance of a fast-moving crate sliding throughout a factory floor and then coming to a sheight. The the majority of advantageous equation for resolving this trouble is A. F  ma. B. Ft  mv C. KE  1/2mv2. D. Fd  1/2mv2. Comment: The work-power theorem is the physicist’s favorite founding suggest for fixing many kind of motion-associated troubles. D. Fd = 1/2mv2. 34 Work-Energy Theorem CHECK YOUR NEIGHBORThe job-related done in bringing a moving automobile to a sheight is the pressure of tire friction  avoiding distance. If the initial speed of the automobile is doubled, the avoiding distance is A.actually much less. around the very same. twice. Namong the over. D. none of the over. 35 Work-Energy Theorem CHECK YOUR ANSWERThe work-related done in bringing a moving car to a stop is the force of tire friction  protecting against distance. If the initial speed of the vehicle is doubled, the preventing distance is A.actually less. about the very same. twice. None of the above. Explanation: Twice the speed indicates 4 times the kinetic energy and four times the protecting against distance. D. namong the above. 36 Conservation of EnergyLaw of conservation of power Energy cannot be developed or destroyed; it may be transcreated from one develop into one more, yet the total amount of power never transforms. 37 Conservation of EnergyExample: Energy transdevelops without net loss or net acquire in the operation of a pile driver. 38 Conservation of Energy A instance to ponder…Consider the mechanism of a bow and arrow. In illustration the bow, we execute occupational on the device and also offer it potential power. When the bowstring is released, most of the potential power is moved to the arrow as kinetic power and some as warmth to the bow. 39 A instance to ponder… CHECK YOUR NEIGHBORSuppose the potential energy of a attracted bow is 50 joules and the kinetic power of the shot arrow is 40 joules. Then A.energy is not conserved. 10 joules go to warming the bow. 10 joules go to warming the taracquire. 10 joules are mysteriously absent. B joules go to warming the bow. 40 A case to ponder… CHECK YOUR ANSWERSuppose the potential energy of a drawn bow is 50 joules and the kinetic energy of the swarm arrowhead is 40 joules. Then A.energy is not conoffered. 10 joules go to warming the bow. 10 joules go to warming the tarobtain. 10 joules are mysteriously absent. Explanation: The complete power of the drawn bow, which includes the poised arrowhead, is 50 joules. The arrowhead gets 40 joules and the staying 10 joules warms the bow—still in the initial device. B joules go to warming the bow. 41 Kinetic Energy and also Momentum ComparedSimilarities between momentum and kinetic energy: Both are properties of moving things. Difference between momentum and kinetic energy: Momentum is a vector amount and also therefore is directional and deserve to be canceled. Kinetic power is a scalar quantity and also deserve to never before be canceled. 42 Kinetic Energy and also Momentum ComparedVelocity dependence Momentum relies on velocity. Kinetic power relies on the square of velocity. Example: An object moving through twice the velocity of one more through the exact same mass, has actually twice the momentum but 4 times the kinetic energy. 43 Machines Machine Device for multiplying pressures or changing the direction of pressures Cannot create energy yet have the right to transdevelop power from one form to another, or transfer energy from one area to one more Cannot multiply work or energy 44 Machines Principle of a maker Conservation of power concept:Work input  job-related output Input force  input distance  Output pressure  output distance (Force  distance)input  (pressure  distance)output 45 Machines Simplest machine Leverrotates on a suggest of assistance dubbed the fulcrum allows small pressure over a big distance and huge pressure over a short distance 46 Machines Pulley operates choose a lever through equal arms— alters the direction of the input force Example: This pulley setup deserve to enable a load to be lifted with half the input pressure. 47 Machines Opeprices as a device of pulleys (block and also tackle)Multiplies force 48 Machines CHECK YOUR NEIGHBORIn an ideal pulley mechanism, a woman lifts a 100-N cprice by pulling a rope downward through a force of 25 N. For eextremely 1-meter size of rope she pulls downward, the cprice rises A.50 centimeters. 45 centimeters. 25 centimeters. None of the above. C centimeters. 49 Machines CHECK YOUR ANSWERIn a perfect sheave system, a womale lifts a 100-N cprice by pulling a rope downward through a force of 25 N. For eincredibly 1-meter length of rope she pulls downward, the crate rises A.50 centimeters. 45 centimeters. 25 centimeters. None of the above. Explanation: Work in = work out; Fd in = Fd out. One-fourth of 1 m = 25 cm. C centimeters. 50 Efficiency EfficiencyPercentage of work-related put into a machine that is converted right into useful work-related output In equation form: Efficiency  beneficial energy output full energy input 51 Efficiency CHECK YOUR NEIGHBORA specific machine is 30% efficient. This means the machine will transform A.30% of the power input to advantageous work—70% of the power input will be wasted. 70% of the energy input to beneficial work—30% of the power input will certainly be wasted. Both of the over. None of the above. A. 30% of the power input to beneficial work—70% of the energy input will certainly be wasted. 52 Efficiency CHECK YOUR ANSWERA specific machine is 30% effective. This indicates the machine will transform A.30% of the power input to useful work—70% of the power input will certainly be wasted. 70% of the power input to valuable work—30% of the power input will certainly be wasted. Both of the above. Namong the above. A. 30% of the power input to valuable work—70% of the energy input will certainly be wasted. 53 Recycled Energy Re-employment of power that otherwise would be wasted. Edison offered warmth from his power plant in New York City to heat buildings. Common power plants waste around 30% of their power to warm bereason they are built ameans from structures and also other places that use warm. 54 Energy for Life Body is a machine, so it demands power.Our cells feed on hydrocarbons that release power as soon as they react via oxygen (choose gasoline melted in an automobile). Tright here is more power stored in the food than in the commodities after metabolism. 55 Sources of Energy Sources of energy Wind SunWind power transforms generator generators. Sun Sunlight evaporates water; water drops as rain; rain flows into rivers and also right into generator turbines; then earlier to the sea to repeat the cycle. Sunlight have the right to be transformed right into electricity by photovoltaic cells. 56 Sources of Energy Sources of power Sun Example:Photovoltaic cells on rooftops catch the solar energy and also transform it to electrical power. More power from the Sun hits Planet in 1 hour than all of the energy consumed by human beings in an entire year! 57 Sources of Energy Fuel cellRuns opposite to a continual battery (where electrical power sepaprices water into hydrogen and also oxygen). In a fuel cell, hydrogen and also oxygen are compressed at electrodes and electrical current is developed at electrodes. 58 Sources of Energy Concentrated power Nuclear powerstored in uranium and also plutonium by-product is geothermal power hosted in underground reservoirs of warm water to provide steam that have the right to drive turbogenerators 59 Sources of Energy Dry-rock geothermal power is a producer of electrical energy. Water is put right into cavities in deep, dry, warm rock. Water turns to heavy steam and also reaches a wind turbine, at the surconfront. After exiting the turbine, it is returned to the cavity for reuse. 