Unit 2 Thermal physics


Notes

Example 4c (iv)

An athlete exerts an average horizontal force on the ground of 30N while running. She runs a distance of 1.6km in 5.0 minutes.

  1. State the equation linking work, force and distance.
  2. Calculate the work the athlete does.
  3. State the equation linking power, work done (or energy transferred) and time taken.
  4. Calculate the power of the athlete.

Answer

  1. work done = force × distance moved or W = F × d
  2. Step 1

    List all the information in symbol form and change into appropriate and consistent SI units if required.

    F=30N

    d=1.6km=1600m

    W=?

    Step 2

    Calculate the answer by putting the numbers into the equation.

      W=  30 × 1600=48000J
  3. power =  work done 

     time taken 
     
      =  energy transferred 

     time taken 
     
      or    
    P =  W 

     t 
     
     
      =  E 

     t 
     
  4. Step 1

    List all the information in symbol form and change into appropriate and consistent SI units if required.

    W=48000J

    t=5.0 × 60s=300s

    P=?

    Step 2

    Calculate the answer by putting the numbers into the equation.

      P=  48000 

     300 
    =160W

    ALWAYS REMEMBER TO STATE THE UNIT FOR CALCULATED QUANTITIES.

 
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