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Homework Help: Confused on these problems

  1. Mar 2, 2006 #1

    For a 3kg object, displacement is given by 6i+3j-4k with a constant force F=2N i + -1N J + 7N k.

    Ive found the total work, but the next question is ' Find the component of F in the direction of this displacement. Answer in units of N. '

    Im really confused as to what is even being asked here. It wants single numerical answer, but it seems as though its asking for the x,y and z compenents of the force. The most logical choice seems that it wants magnitude of the Force, but this is wrong.


    A civil engineer is asked to design a curved
    section of roadway that meets the following
    With ice on the road, when the coffcient of
    static friction between the road and rubber is
    0.25, a car at rest must not slide into the ditch
    and a car traveling less than 50 km/h must
    not skid to the outside of the curve.
    The acceleration of gravity is 9.81 m/s^2

    At what angle should the road be banked?
    Answer in units of degress.

    This problem completely leaves out the radius, and without radius Im unsure how to solve this, can anyone offer some help as how to go about solving this?
  2. jcsd
  3. Mar 2, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    First - the problem is to find the F component in the direction of 6i+3j-4k.

    Find the unit vector in the direction of 6i+3j-4k, and then . . . .

    Secondly - use the static part of the problem to find the banking angle.

    With the banking angle, determine the radius that a car can travel without sliding to the outside of the curve.
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