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Average velocity of clock hand

  1. Jun 10, 2009 #1
    The minute hand of a clock is 5.5 cm long. What is average velocity vector for the tip of the hand during the interval from the hour to 20 minutes past the hour, expressed in a coordinate system with they-axis toward noon and x-axis toward 3 o'clock? (Answer in terms of i-hat and j-hat components please)
     
  2. jcsd
  3. Jun 10, 2009 #2
    Everyone here has helped me so much, so I will do the same. Ok you know that in 20 minutes, the minute hand moves 1/3 of the circle. Therefore it moves 120 degrees. Drawing a picture helps here. Now you have a isosceles triangle with sides 5.5 and vertex angle 120. Solve to get the other side and divide by 20 for an answer in cm/min.
     
  4. Jun 11, 2009 #3
    Velocity is equal: v=r x ω
    ω is the angular velocity of the minute hand. You know that the minute hand makes 2pi in one minute (60 seconds). So angular velocity is equal: ω= 2*pi/60 = 1/60 pi.
    Velocity (perpendicular on the minute hand) is equal to :v=r x ω=0,055 * 1/60 pi.
    Velocity in i & j is v= vxi + vyj.
    vx=-v*cos60
    vy=-v*sin60
    (I have attached a photo)
     

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