Power

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Power

• The Crab Nebula,
• supernova remnant

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Power

• Like work, weve all heard about power
• But what is it?

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Power Work / Time

• Scientists define power as the amount of work
  done divided by the time it takes to do that work
• Power is works rate of change

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Definition 2

• As work is related to energy, we can also define
  power as the rate of energy use
• Power Change in Energy/Elapsed Time

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Units

• The units of power are Joules/seconds
• 1J/s 1 Watt (W)
• So if you lift your 1lb weight 10inches in the
  air in 1second, your power is 1watt

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Power Comparisons

• Light Bulb 100 W
• Vacuum Cleaner
  1,500 W
• Dodge Ram w/ Hemi 250,000
  W
• Space Shuttle 11,000,000,000 W
• Sun 400,000,000,000,000,000,000,000,000 W

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Question

• A machine does 200J of work over a time interval
  of 20s. What is this machines power?
• 10W

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How much Energy does a 40W light bulb consume in
2 minutes?
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Machine A performs a certain amount of work in
time t. Machine B performs twice as much work as
1, but takes 4 times as long. Machine C performs
the same amount of work as 1, but in ½ the time.
Rank the power of each machine in increasing
order.

• 1. A, B, C 2. C, B, A
• 3. C, A, B 4. B, A, C
• 5. B, C, A

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Using a 40N force, a pulley system pulls a box
forward at a constant velocity of 2m/s. What is
this pulley systems power?
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