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Help with these HW problems involving grav acceleration, circular motion, etc?

  1. Sep 21, 2009 #1
    1) Estimate the force a person must exert on a string attached to a 0.100 kg ball to make the ball revolve in a circle when the length of the string is 0.600 m. The ball makes 1.00 revolutions per second. Do not ignore the weight of the ball. In particular, find the magnitude of FT, and the angle ϕ it makes with the horizontal. [Hint: Set the horizontal component of FT equal to maR; also, since there is no vertical motion, what can you say about the vertical component of FT?]
    FT= 2.368705056(Your answer is incorrect.) N [Why is that not right? I feel as if I've forgotten something]
    ϕ= °


    2) A car at the Indianapolis-500 accelerates uniformly from the pit area, going from rest to 285 km/h in a semicircular arc with a radius of 194 m.
    Determine the tangential acceleration of the car when it is halfway through the turn, assuming constant tangential acceleration.
    Answer= m/s2
    Determine the radial acceleration of the car at this time.
    Answer= m/s2
    If the curve were flat, what would the coefficient of static friction have to be between the tires and the roadbed to provide this acceleration with no slipping or skidding?
    Answer=


    3) What is the distance from the Earth's center to a point outside the Earth where the gravitational acceleration due to the Earth is 1/14 of its value at the Earth's surface?
    Answer= m

    4) What will a spring scale read for the weight of a 66 kg woman in an elevator that moves as follows?
    A) upward with acceleration of 0.31g? [in newtons]

    B) downward with acceleration 0.31g? [in newtons]


    I am NOT asking for you guys to do them for me. Instead, I would like it if you guys can help me get started by pointing out what steps I should use to get these done. Thank you.
     
    Last edited: Sep 21, 2009
  2. jcsd
  3. Sep 21, 2009 #2
    I got that one. It was a problem with the picky rounding the HW website has. I'm still lost on the others, though.
     
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