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Circular Motion

  1. Jan 18, 2006 #1
    1. The speed of a car travelling on a straight horizantal road is v. What is the speed of point P on the tyre of the car?

    I consider the distance travelled by the car per revolution is same as the circumference of the tyre, while speed of point P, is equals to circumference divided by the time taken. If that so, the speed of the point P = v.
    But the answer given is 2v. What method should I use to determine speed of the point P?

    2. An aircraft is flying in a horizantal circle of radius 80km at a constant speed of 300ms-1. What is the ratio of the lift on the aircraft to its weight?

    The angle is not given here. How should I calculate the lift?
  2. jcsd
  3. Jan 18, 2006 #2
    I think point p is a point at the "top" of the tire.
    The velocity of the center of the tire is v.
    The tangential velocity of the rim of the tire is v.
    Hence v+v=2v.
    On the other hand, the point which the the tire contact with ground has velocity 0, since the the tangential velocity of the rim is opposite to translate velocity. So v-v=0
  4. Jan 18, 2006 #3
    :smile: Yeah, the point P is located at the top of the tyre. It is in the diagram given but unfortunately i can't show it. I thought the speed at the point P is the tangential velocity, no wonder I can't find the correct answer.

    Thanks for curing my headache:smile: .
  5. Jan 18, 2006 #4
    hey for the second part of the question, I would have thought you would have to consider the centripetal force and resolve it with respect to the lift and the weight

    Due to the fact that you are now dealing with ratios the masses should cancel.

    Centripetal force=mv^2/r

    I think this is correct

    correct me if I am wrong
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