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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 machines
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 machines1
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
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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slide5

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
3. When you ride a playground swing, your potential energy is greatest at the highest point.
  • True
  • False
energy work power machines2
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 machines3
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
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
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
7. The metric unit for power is a _____________.
  • a. Joule
  • Watt
  • Newton
  • 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
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
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
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
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
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
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
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 machines4
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 machines5
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 machines6
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
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 machines7
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
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
10. Which pulley has the greatest mechanical advantage?
  • A. Picture 1
  • B. Picture 2
  • C. Picture 3
  • D. Picture 4

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