Work, Power, and Efficiency

What is the definition of power?

• Power is a comparison of how much energy is used to do work versus how much is lost or wasted to the environment.

• Power means that you are in charge.

• Power is the ability to lift things up and put them down.

• Power is the rate at which someone, or something, uses energy.

What is the unit for Power?

• Joules

• Volts

• Watts

• Amps

If Mr. P runs up a flight of stairs with a height of 10 meters in 5 seconds and Mr. P’s twin brother who has the same mass runs up the same flight of stairs in 4 seconds. Who has more power?

• Ms. Poteete

• Mr. P

• Mr. P's twin brother

• Ms. Millard

If Mr. P’s dog Ally has a mass of 50 kg and runs up a flight of stairs with a height of 10 meters in 2 seconds and Ms. Poteete’s dog Jasper has a mass of 25 kg and runs up the same flight of stairs in the same amount of time. Which dog has more power?

• Jasper

• Ally

• Air Bud

• Scout

How much wasted energy is there in this Sankey diagram?

• 100 J

• 75 J

• 50 J

• 25 J

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If a light bulb with an efficiency of 80% lights up the room and 16 J of energy is converted to light energy and 4 J of energy is lost to thermal energy. What is the total energy in the system?

• 80%

• 4 J

• 20 J

• 16 J

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An engine has an inout of 5000 W. The useful output is 4000W. Calculate its percentage efficiency.

• 90%

• 80%

• 75%

• 85%

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A washing machine uses 250J of electrical energy to produce 125J of useful energy. How efficient is it?

• 5%

• 50%

• 55%

• 100%

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How much time is needed to produce 720 Joules of work if 90 watts of power is used? 

• 0.125 s
• 8 s
• 64800 s
• 80 s

If 150 Joules of work is needed to move a box 10 meters, what force was used? 

• 1500 N
• 15 N
• 1.5 N
• 150 N