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Trigonometeric Ratios: Tire Speed

  1. Apr 14, 2005 #1
    Can someone get me started? This is a homework question that I just can't get started on.

    No wonder it's a "challenge" question.

    A car is travelling at 100km/hr.

    A) What is the angular speed of a tire which has a radius of 36cm.

    B) Through how many radians will the tire turn in 30s at this speed?
  2. jcsd
  3. Apr 14, 2005 #2
    100km/hr = 360m/s

    In one second, it travels 360m. Think of the distance along the tire rim travelled.
    Can you find how many revolutions it completes in one second? (360m).
  4. Apr 14, 2005 #3


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  5. Apr 14, 2005 #4
    Did I butcher it?

    100km/hr * 1hr/3600s * 1000m/1km = 27.77m/s

    Yes I did. Sorry.
  6. Apr 14, 2005 #5
    Wouldn't I need to divide the circumfrence by the speed?


    so, 360/2.26 = 159.2920 rotations/sec. That's wrong.

    Because then 2pi, for one whole rotation would be
    318.5841pi/1sec = 1000.86 radians/sec

    Yeah, ok. What's wrong. =P :rofl:

    Edit: I redit the question the same way except I substituted 27.77 for 360. I got 38.something. Which isn't right either.
    Last edited: Apr 14, 2005
  7. Apr 14, 2005 #6


    27.77/2.26 = xxx rev/s

    Its going to be about 12-13
  8. Apr 14, 2005 #7
    yeha, sorry - I got that much. The 38 was from the calculation to get ther radians/sec

    12.2876pi/sec = 38.6027 ... Yeah I don't know what I'm doing there.
  9. Apr 14, 2005 #8
    27.77m/s * 1rev/2.26m = 12.28rev/s
    1 revolution = 2pi radians

    12.28 rev = 75.4 radians

    12.28rev/s = 75.4rad/sec

    God now your confusing me. I'm going to bed, lol.
    Last edited: Apr 14, 2005
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