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Homework Help: Car curves at a radius of 50m while travelling at 100km/hr

  1. Nov 13, 2011 #1
    1. The problem statement, all variables and given/known data

    Calculate the centripetal acceleration module in the following cases as a multiple of g = 9.8 m / s ^ 2.
    a) a car traveling at 100km / h on a curve of radius 50m.
    b) a jet plane flying at 1,500 km / h and making a turning radius of 5km.
    c) a stone that is rotated every 0.5 s after a string of length 1 m
    d) a speck of dust on the edge of a disk of 30 cm diameter rotating at 33.33333 ... rev / min.
    e) a molecule in a centrifugal radius of 15cm rotating at 30,000 rev / min.

    2. Relevant equations

    g= 9.8 m/s2
    ar = v2/r
    ar = ug

    u: coefficient of friction(WHERE DO I GET THIS?!)

    haven't touched b) and on yet..

    3. The attempt at a solution
    so heres how i began...
    vi = 100km/h = 10 000m/3600s = 27,78m/s
    ar= 1002/50 = 200 m/s2

    ar = 9,8u

    Okay... so how do i get the coefficient of friction(u) if im not given any mass value?
  2. jcsd
  3. Nov 14, 2011 #2
    You don't need the coefficient of Friction for these problems. Convert the velocity to m/s. Square it and divide by the radius in meters to get ac. Divide by 9.8 to get the multiple.

    You will need to find the angular velocity for some of these problems and be able to convert from revolutions/min to radians/sec
  4. Nov 14, 2011 #3
    That's awesome, thanks! I got a, b, and c, but im stuck on d ... given its diameter, where do i go from there?
    Last edited: Nov 14, 2011
  5. Nov 14, 2011 #4
    Remember that ac=r*ω2 you have r you need to find ω, the angular velocity. The units are radians/sec. The stone makes 1 revolution in .5 seconds. 1 revolution is how many radians? Divide that number by 0.5 sec
  6. Nov 14, 2011 #5
    I got it, thanks!
  7. Nov 14, 2011 #6
    I'm doing the d right now...
    found that r= 0,015m
    w = 0,349 rad/s
    and used the equation:
    and got ac= 0,0018

    then divided it by 9,8.... and got 1,84 x10^-4g........ when the right answer should just be 1,87g
    Last edited: Nov 14, 2011
  8. Nov 14, 2011 #7
    radius is not .015m
    ω is not .349 rad/s
    Recheck these values and recalculate
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