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					   Power

  Chapter 5
Honors Physics
     Which does more Work?



5s             10 s
         Power
Rate at which work is done


         W
      P
         t
             Power Units                    Quic kTim e™ and a TIFF (Unc ompress ed) decompres sor are needed to s ee this pic ture.




MKS - J/s = W (Watt)
English - ft lb /s
550 ft lb / s = 1 hp   QuickTime™ and a T IFF (Uncompressed) decompressor are needed to see this picture.




1 hp = 746 W
Another look at Power

   Fx
P      Fv
    t
       Work Practice Problems
6. A student with a mass of 80.0 kg runs
up three flights of stairs in 12 s. The
student has gone a vertical distance of
8.0 m. What is the student’s power?

7. a 9.0 kW motor lifts a 3500 kg elevator
to a height of 9.5 m. How long does it
take?
What is the kWh?

 A unit of Energy
        Center of Mass (CM)
• A person has a mass which is spread
  throughout the body
• CM is the point at which all mass is
  considered to be concentrated
Review - Work by Varying Force

				
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