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ENERGY,WORK, POWER, AND MACHINES IPC Spring 2014

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Energy, Work, Power & Machines 1. Energy is the ability to do work. Potential energy – stored energy or energy due to position 1. Energy is the ability to do work. Potential energy – stored energy or energy due to position PE=m g h PE=m g h m is mass (kg) m is mass (kg) g is gravity (9.8 m/s 2 ) g is gravity (9.8 m/s 2 ) h is the height of the object (m) h is the height of the object (m) Kinetic energy – energy of motion KE= mv 2 /2 KE= mv 2 /2 m is mass (kg) m is mass (kg) v is velocity (m/s) v is velocity (m/s)

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Energy, Work, Power, & Machines 2.Energy conversion is a changing of one form of energy to another. 2.Energy conversion is a changing of one form of energy to another. 3.The Law of Conservation of Energy states that energy cannot be created nor destroyed, but is only changed from one form to another. 3.The Law of Conservation of Energy states that energy cannot be created nor destroyed, but is only changed from one form to another.

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1. After you place a book on a high shelf, we say the book has increased _____. A. gravitational potential energy. B. elastic potential energy. C. chemical energy. D. kinetic energy.

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2. An empty truck traveling at 10 km/h has kinetic energy. How much kinetic energy does it have when it is loaded so its mass is twice, and its speed is increased to twice? A. the same KE B. twice the KE C. four times the KE D. more than four times the KE

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3. When you ride a playground swing, your potential energy is greatest at the highest point. A. True B. False

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4. As mass decreases, kinetic energy increases. A. True B. False

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Energy, Work, Power, & Machines 4.Work is done when a object moves through a distance because of a force acting upon the object. 5.The following formula is used to calculate work: W=F×d. W stands for the work done (J) F stands for the force (N) d stands for distance (m) The SI unit for work is the joule (J). The SI unit for work is the joule (J).

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Energy, Work, Power, & Machines 6.Power - the rate at which work is done. 7.Power can be calculated by using the following formula: P= W/tor P = F×d/t P stands for power (W) W stands for work (J) t stands for time. (s) The SI unit for power is the watt (W).

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5. A student weighing 900 N runs to the top of an 8 m staircase in 5 sec. How much power was produced? A. 56.25 W B. 11.25 W C. 1440 J D. 1440 W

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6. The metric unit for work is the _________________. A. Watt B. Joule C. Newton D. Foot-Pound

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7. The metric unit for power is a _____________. A. a. Joule B. Watt C. Newton D. Horsepower

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8. How much work does Billy perform if he pushes the 8000 N stalled car a distance of 25 meters? A. 320 J B. 100,000 J C. 200,000 J D. 8025 J

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Simple Machines

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Inclined Plane A plane is a flat surface. When that plane is inclined, or slanted, it can help you move objects across distances and that's work! A common inclined plane is a ramp. Lifting a heavy box onto a loading dock is much easier if you slide the box up a ramp--a simple machine.

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Wedge You can use the edge of an inclined plane to push things apart. Then, the inclined plane is a wedge. So, a wedge is actually a kind of inclined plane. An axe blade is a wedge. Think of the edge of the blade. It's the edge of a smooth slanted surface.

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Screw screw A screw an inclined plane wrapped around a cylinder torque torque A screw can convert a rotational force (torque) to a linear force and vice versa.torque

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Lever lever Any tool that pries something loose is a lever. A lever is a rigid bar that "pivots" (or turns) against a "fulcrum" (or a fixed point).

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Wheel and Axle It is two circular objects attached together about a common axis Wheel is the large cylinder Axle is the small cylinder

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Pulley In a pulley, a cord wraps around a wheel. As the wheel rotates, the cord moves in either direction. Now, attach a hook to the cord, and you can use the wheel's rotation to raise and lower objects.

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Energy, Work, Power, & Machines 8.The mechanical advantage is the number of times a machine multiplies an effort force. Mechanical advantage can be calculated by the following equations: AMA = F r IMA = d e F e d r AMA = actual mechanical advantage (real life) IMA = ideal mechanical advantage (pretend) F r = resistance forced e = effort distance F e = effort forced r = resistance distance 9. The mechanical advantage of a pulley system is determined by counting the number of strands of rope that support the resistance force.

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Energy, Work, Power, & Machines 10.Work input is always greater than work output due to friction. W in = W out F e x d e = F r x d r W in = work input (J) W out = work output (J) F e = effort force (N) d e = effort distance (m) F r =force of the resistance (N) d r =how far the resistance moved (m)

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Energy, Work, Power, & Machines 11.Efficiency is a measure of how much of the work put into a machine is changed to work put out by the machine. Efficiency is calculated using the following formula: efficiency = W out x 100% W in efficiency =AMAx 100% IMA

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Efficiency of a Machine 12.The amount of work obtained from a machine is always less than the amount of work put into it. This is because work is lost to friction. Efficiency = output work / input work x 100 Remember that work = force x distance

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Energy, Work, Power, & Machines 13. Compound machines consist of two or more simple machines.

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9. When 100 J are put into a device that puts out 40 J, the efficiency of the device is A. 40%. B. 50%. C. 60%. D. 140%.

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10. Which pulley has the greatest mechanical advantage? A. A. Picture 1 B. B. Picture 2 C. C. Picture 3 D. D. Picture 4

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