ENERGY,WORK, POWER, AND MACHINES

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ENERGY,WORK, POWER, AND MACHINES. IPC Spring 2014. Energy, Work, Power & Machines. 1. Energy is the ability to do work. Potential energy – stored energy or energy due to position PE=m g h m is mass (kg) g is gravity (9.8 m/s 2 ) h is the height of the object (m )

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### ENERGY,WORK, POWER, AND MACHINES

IPC Spring 2014

Energy, Work, Power & Machines

1. Energy is the ability to do work. Potential energy – stored energy or energy due to position

• PE=m g h
• m is mass (kg)
• g is gravity (9.8 m/s2)
• h is the height of the object (m)

Kinetic energy – energy of motion

• KE= mv2 /2
• m is mass (kg)
• v is velocity (m/s)
Energy, Work, Power, & Machines
• 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.
1. After you place a book on a high shelf, we say the book has increased _____.
• gravitational potential energy.
• elastic potential energy.
• chemical energy.
• 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?

• the same KE
• twice the KE
• four times the KE
• 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.
• True
• False
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).
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).
5. A student weighing 900 N runs to the top of an 8 m staircase in 5 sec. How much power was produced?
• 56.25 W
• 11.25 W
• 1440 J
• 1440 W

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6. The metric unit for work is the _________________.
• Watt
• Joule
• Newton
• Foot-Pound

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7. The metric unit for power is a _____________.
• a. Joule
• Watt
• Newton
• Horsepower

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8. How muchwork does Billy perform if he pushes the 8000 N stalled car a distance of 25 meters?
• 320 J
• 100,000 J
• 200,000 J
• 8025 J

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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.

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.
Screw

A screw an inclined plane wrapped around a cylinder

A screw can convert a rotational force (torque) to a linear force and vice versa.

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).
Wheel and Axle
• It is two circular objects attached together about a common axis
• Wheel is the large cylinder
• Axle is the small cylinder
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.
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 = Fr IMA = de

Fedr

• AMA = actual mechanical advantage (real life)
• IMA = ideal mechanical advantage (pretend)
• Fr = resistance force de = effort distance
• Fe = effort force d 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.
Energy, Work, Power, & Machines
• 10.Work input is always greater than work output due to friction.

Win= W out

Fe x de = Fr x d r

• Win = work input (J)
• W out=work output (J)
• Fe= effort force (N)
• de= effort distance (m)
• Fr =force of the resistance (N)
• d r=how far the resistance moved (m)
Energy, Work, Power, & Machines
• 11.Efficiencyis 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%

Win

• efficiency = AMA x 100%

IMA

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

Energy, Work, Power, & Machines
• 13. Compound machines consist of two or more simple machines.
9. When 100 J are put into a device that puts out 40 J, the efficiency of the device is
• 40%.
• 50%.
• 60%.
• 140%.

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

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