1. Limited time only! Sign up for a free 30min personal 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!

Mistake in Dynamics Circular Problem's Solution

  1. May 22, 2014 #1
    Please look at pictures.
    I do not understand the solutions;

    Here is how I find length of string:
    5m/s*1.2s/rev=6m/rev=circumference=2piR
    R=0.95m.


    For the force:
    T=mv^2/r= 0.350 kg *5^2/0.95= 9.21N They got 9.16N?
     

    Attached Files:

  2. jcsd
  3. May 22, 2014 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    The numbers in the problem are stated to 3 significant figures. So, make sure you keep at least 3 significant figures in your intermediate calculations. What do you get for R to 3 significant figures?
     
  4. May 22, 2014 #3
    Well the answer I got is 0.95m which is almost twice as big as the radius they found.
    I keep all my sig figs on my calculator.
     
  5. May 22, 2014 #4
    I don't know what is going on! :O
     
  6. May 22, 2014 #5

    TSny

    User Avatar
    Homework Helper
    Gold Member

    You got R = .95 m. That has only 2 significant figures. What do you get to 3 significant figures?

    When you calculated T, it looks like you used r = .95 m. Again, only 2 significant figures for r. What do you get for T if you use a value for r that is accurate to 3 significant figures?
     
  7. May 22, 2014 #6

    TSny

    User Avatar
    Homework Helper
    Gold Member

    OK, I did not see the answer they had for R. Their answer is wrong, yours is right. But you should give it to 3 significant figures.
     
  8. May 22, 2014 #7
    R=0.955m.
    T=9.16N. You were right! Ok. This was my bad.
    What about the radius? The radius they report is definitely wrong?
     
  9. May 22, 2014 #8
    Perfect! Everything works out great!
     
  10. May 22, 2014 #9

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Good!
     
  11. May 22, 2014 #10

    ChrisVer

    User Avatar
    Gold Member

    their radius is mistyped- probably 4 was meant to be a 9....
    as for the rest, follow TSny's post
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted