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Homework Help: Work problem with vector notation! Help please

  1. Dec 10, 2009 #1
    1. The problem statement, all variables and given/known data
    PART A: A force ~F = Fx ˆı+Fy ˆ acts on a particle that
    undergoes a displacement of ~s = sx ˆı + sy ˆ
    where Fx = 6 N, Fy = −3 N, sx = 5 m, and
    sy = 1 m.
    Find the work done by the force on the
    particle.
    Answer in units of J.

    PART B: Find the angle between ~F and ~s.
    Answer in units of ◦.

    PART C: An easy question but still need help:
    Which of the following does not involve work?
    1. A golf ball is struck.
    2. A weight lifter does military presses (lift-
    ing weights over his head.)
    3. A professor picks up a piece of chalk from
    the floor.
    4. A runner stretches by pushing against a
    wall.
    5. A child is pushed on a swing.

    2. Relevant equations
    a^2+b^2=c^2
    F=ma
    W=fcosthetad

    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 10, 2009 #2
    so here's my try: i made two triangles...one out of the force vectors and another out of the displacement vectors
    i found the resultant displacement vector to be 5^2+1^2=26...so 5.1 m
    i found the resultant force vector by doing 3^2+6^2=45...so 6.7 N

    if i plug in these numbers into the work equation of W=fdcostheta i'll get W=5.1m*6.7Ncostheta
    to find theta i'll do the tantheta=1m/5m or 11.3099 degrees or 348.69 degrees when put in the correct coordinate plane....
    so does W=5.1m*6.7Ncos348.69? that equals 33.5 joules.
     
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