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Homework Help: Circular motion velocity

  1. Sep 15, 2010 #1
    1. The problem statement, all variables and given/known data

    The sweep-second hand of a clock is 3.1 cm long.
    What are the magnitude of (a) the average
    velocity and (b) the average acceleration of the
    hand’s tip over a 5.0-s interval? (c)what is the angel between the average velocity and acceleration vectors?

    2. Relevant equations
    a= v2/r

    3. The attempt at a solution
    Ok so I have been working on this problem for about an hour and its starting to annoy me I can't seem to find the velocity vector since I am not given a time frame besides the one for the acceleration. I know that I can find acceleration as soon as I find velocity but I don't have any formulas or any thought on how to go about solving for average velocity. I also know that the answer for part c is 90 degrees since they are always perpendicular so really its just part a that is giving me so much trouble.
  2. jcsd
  3. Sep 15, 2010 #2


    User Avatar

    Here are a couple of hints: (1) The time frame for the velocity and the acceleration is the same: 5 sec. (2) Find the distance that the tip of the second hand travels in 5 sec. You can do this by knowing that it travels 360 degrees, or 2 Pi radians in 60 seconds. From that tells you can figure out the angle it travels in 5 sec. Then use Distance = radius times angle (in radians). That allows you to calculate the velocity and so on.
  4. Sep 15, 2010 #3
    This was extremely helpful I forgot that you could find it in this way thank you so much.
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