1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Calculating Horsepower/Torque from Acceleration/Mass
  1. Calculating Horsepower (Replies: 2)

Loading...