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Homework Help: Motorsport Technolgy Vehicle Analysis.

  1. Dec 21, 2009 #1
    1. The problem statement, all variables and given/known data

    Hi im new here and really struggle with maths/physics based problems as i have very little experience in them due to studying other subjects at A-Level and now studying Motorsport Tech at uni.

    This is the questions we have been set for xmas work.

    A rear wheel drive car of mass 2200kg has a rolling resistance of 150 N, a frontal area of 1.6m2, a drag coefficient of 0.30, a transmission loss of 10% and a maximum engine power of 75kW. Assuming that the traction limit for each tyre is equal to the weight that it carries (i.e. the tyre traction coefficient =1) and that 60% of the vehicle weight is on the rear wheels during acceleration,

    a) What is the maximum power available at the back wheels?

    b) What is its theoretical maximum speed in mph on a level road?

    c) What is its theoretical maximum speed in mph up a 1 in 4 hill?

    d) What is the maximum tractive force that each of the rear tyres could provide under acceleration before slipping occurs? (NB this is per rear wheel not per axle !!)

    e) What would be the maximum, useable, tractive force at each of the rear tyres if full power was applied at 25 mph? (hint: is this limited by tyre grip or by engine power?)

    f) What would be the wind resistance at 25 mph?

    g) What would be the acceleration (in mph/s) at 25 mph on the level?

    h) What would be the acceleration (in mph/s) at 25 mph up a 1 in 4 hill?

    Take the density of air to be 1.2 Kg/m3 and g = 9.8 m/s2

    2. Relevant equations

    Instead of asking for answers to these questions i would just like a nudge in the right direction as i am unsure as to which equations to use as we havnt really been given many yet?

    D = 0.5 **V2*Cd*A

    D is the air resistance (drag) in Newtons
     is the air density (about 1.2Kg/m3 at sea level)
    V is velocity in m/s
    Cd is the drag coefficient
    A is the frontal area of the vehicle in m2

    0.5 = 0.6 kg/m3

    dont know if that is useful?

    3. The attempt at a solution

    All my attempts have resulted in a mess so far, for question one i hazard a guess that you just have to remove 10% or do i need to include other factors?

    Thanks in advance for any help, This doesnt have to be in until the 12th jan so i have a while to go through it with as much help from you guys as possible


  2. jcsd
  3. Dec 21, 2009 #2
    I will update with work i have tried to do as i am giving this as much effort as i can im just terrible at this sort of work.

    Q1. I removed 10% leaving me with power at rear wheels as 67.5 kW or 67500 w

  4. Dec 21, 2009 #3


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    Staff: Mentor

    Looks correct for Q1.

    Welcome to the PF, BTW.
  5. Dec 21, 2009 #4
    Thanks mate, hope i have posted in correct section etc and not been to cheeky in posting all the questions its just that ive sat here since eight this morning and im getting frustrated lol
  6. Dec 21, 2009 #5
    In questions 2 and 3 would you say that "theoretical" means i dont have to include resistance etc?
  7. Dec 23, 2009 #6
  8. Dec 23, 2009 #7


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    Staff: Mentor

    Not sure what they mean by "theoretical" in b) and c). It could be neglecting air resistance and rolling resistance, but you have the tools to calculate those, so I'm not sure. Maybe calculate it both ways (with and without resistance) and label the answers, just to be sure.
  9. Dec 24, 2009 #8
    ok cheers mate, its a digital answer form were u can only put one answer, so il have to think, ive sent my tutor an email so will wait for his reply! can anyone shed light on equations i might use for the other questions?

    Thanks again

  10. Jan 1, 2010 #9
    Im not making much progress with this. . .:eek:
  11. Jan 1, 2010 #10


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    Staff: Mentor

    What was your tutor's reply to your e-mail?
  12. Jan 1, 2010 #11
    Hasnt replyed yet, im only hoping he will soon!
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