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Homework Help: Projectile motion and circular motion questions

  1. Oct 6, 2005 #1
    Ok I have two questions which I am stuck on. I just need some hints.

    1.)An airplane is flying with a velocity of 90.0 m/s at an angle of 23.0m\s above the horizontal. When the plane is a distance 115 m directly above a dog that is standing on level ground, a suitcase drops out of the luggage compartment.

    q.)How far from the dog will the suitcase land? You can ignore air resistance

    For this one I think I have to calculate the time it takes for the suitcase to hit the ground. And then I can use d=vt to calculate the distance away from the dog. But i am having a problem with the intial velocity in the y direction. When the suitcase falls off the plane its intial velocity is not zero right. Its inital velocity will be the same as the plane right.

    2.)A model of a helicopter rotor has four blades, each of length 3.60 m from the central shaft to the blade tip. The model is rotated in a wind tunnel at a rotational speed of 530rev/min.
    q1.)What is the linear speed of the blade tip?
    q2.)What is the radial acceleration of the blade tip expressed as a multiple of the acceleration of gravity, g?

    Really dont know where to start out on this one, just point me in the right direction.

  2. jcsd
  3. Oct 6, 2005 #2


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    Homework Helper

    1) Right general idea. Split the velocity of the plane into horizontal and vertical components and you're pretty much set to go.

    2) For part 1, think about how far the blade tip has to go to complete one revolution, then how long it takes for it to complete said revolution.

    For part 2, would it help if I pointed out that that's the centripetal acceleration?
  4. Oct 6, 2005 #3
    Hey thanks,

    For the first question I was using 115 m instead of negative. Thats why i kept getting it wrong.

    And for question 2, I didn't think about the circumference until you stated it. And i figured out the acceleration as well.
  5. Jul 27, 2010 #4
    what are the answers to these questions?
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