1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Velocity of an Object in Uniform Circular Motion

  1. Oct 5, 2014 #1
    1. The problem statement, all variables and given/known data
    An object of mass 0.5 kg is swung in uniform circular motion. The radius is 2 meters, and the force exerted is 4 N. Calculate the magnitude of the velocity.

    Answer Choices:
    a) 0.25 m/s
    b) 1 m/s
    c) 4 m/s
    d) 16 m/s

    2. Relevant equations
    v = 2piR/T
    F = mv^2/R

    3. The attempt at a solution
    Since I didn't know the variable time, I couldn't use the velocity equation. Next, I tried plugging in the variables for the centripetal force equation and solving for velocity:

    4 = (0.5)v^2/2
    4 = 0.5/2 + v^2/2
    4 = 0.3 + v^2/2 <- 0.3 because of significant figures
    (subtracted 0.3 from both sides)
    4 = v^2/2 <- 4 because of significant figures
    (multiplied both sides by 2)
    8 = v ^2
    (took the square root of both sides)
    v = 3 which isn't one of my answer choices.

    Maybe I'm not doing my algebra correctly or maybe I'm not using the right equation, but I couldn't find another equation using the variables I have. If I knew the time it took for one revolution I could use the velocity equation, but I don't know how to find time and I couldn't find an equation for finding it.
     
  2. jcsd
  3. Oct 5, 2014 #2
    There is an algebra mistake in going from the first to the second step. You have essentially turned a product into a sum instead.

    On a side note, when taking significant figures into account, do so only on the final answer. If you keep rounding off at each step, you will find that the rounding-off error grows substantially larger after each step, and the final answer you obtain might be significantly off the correct one.
     
  4. Oct 5, 2014 #3
    Ohh, okay, that makes a lot more sense. I'll be sure to keep that in mind about significant figures in the future, too.

    Thanks a lot!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Velocity of an Object in Uniform Circular Motion
Loading...