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Homework Help: Simple Power calculation

  1. Mar 7, 2012 #1
    Can anyone see where i have went wrong? I keep getting the same wrong answer.

    A 1100 kg car accelerates from rest reaching a distance of 110 m in 8.7 seconds, determine the average power in KW required to achieve this acceleration (your answer should be to 2 decimal places).

    ANS = 40.43
    MY ANS = 20.21

    Working out

    V = d/t
    V= 110/8.7 = 12.64

    Acc = (12.64 - 0) / 8.7 = 1.45

    Force = ma
    Force = 1100 x 1.45 = 1598.63

    Work done = force x distance
    Work done = 1598.63 x 110 = 175848

    Power = WD/T
    Power = 175848/8.7 = 20.21KW

    Thanks
     
  2. jcsd
  3. Mar 7, 2012 #2
    The velocity is not constant here,
    you should use s = ut + [itex]\frac{1}{2}[/itex]at2 instead
     
  4. Mar 7, 2012 #3
    Thanks for your reply.
    How do i use this formula if i have two unknowns for V and a
     
  5. Mar 7, 2012 #4
    You just have to find a and carry on with F=ma

    P.S. I gave you the wrong formula just now :P
     
  6. Mar 7, 2012 #5
    Got it, thanks mate
     
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