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Homework Help: Calculating Horsepower/Torque from Acceleration/Mass

  1. May 1, 2006 #1
    Apologies in advance if this is not the correct forum.

    This is (what seems to me) an old question people have been playing with for a while, but I dont seem to be able to figure out where I have gone wrong.

    Could someone point out the mistake in my math from the following example:

    Constant Mass = 1180Kg

    Sample 1 @ 2 secs
    Kilometers/Hour = 37
    Meters/Sec = 10.278
    RPM = 3000

    Sample 2 @ 3 secs
    Kilometers/Hour = 46
    Meters/Sec = 12.778
    RPM = 3780

    Sample 3 @ 4 secs
    Kilometers/Hour = 59
    Meters/Sec = 16.389
    RPM = 4860


    Using the formula: KE = (1/2)(m)(v^2) I calculated

    KE1 = 0.5 * 1180 * (10.278 * 10.278) = 62326 ??Joules??
    KE2 = 0.5 * 1180 * (12.778 * 12.778) = 96333.6 ??Joules??
    KE3 = 0.5 * 1180 * (16.389 * 16.389) = 158473.6 ??Joules??

    Using the formula: W = (KE / Time) given the sampling time is 1sec
    W = KE.

    Converting (roughly) from W (watts) to HP: HP = W / 746

    HP1 = 83.54
    HP2 = 129.12
    HP3 = 212.32

    I know from another piece of software that the correct values should be:

    HP1 = 59
    HP2 = 76
    HP3 = 105


    Could someone be kind enough to point out my fault. Greatly appreciated.

    Tony
     
  2. jcsd
  3. May 1, 2006 #2

    Hootenanny

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    Could you start by stating the question exactly as it is given please.

    ~H
     
  4. May 1, 2006 #3
    The question is:

    Plot a graph showing horsepower at given time intervals based on sampled data.


    There are actually 10 samples, but I have only included 3 for simplicity. The original data only included Time, Kilometers/Hour and RPM (although I don't think RPM is needed for this part of the question). I converted KPH to meters/sec as I think this is the correct unit for KE.
     
    Last edited: May 1, 2006
  5. May 1, 2006 #4

    Hootenanny

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    And you have no other information regarding the vehical?

    ~H
     
  6. May 1, 2006 #5
    I was given the vehicle weight of 1180kg, and the time-sampled data, but nothing else.
     
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