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!

What is the approximate weight of a 20.kg rock

  1. Feb 1, 2012 #1
    Since it has a decimal it would be 20kg * 9.8m/s which equals 196kg m/s^2 = 196N

    But the decimal means i have to round two sig figs, which would make it 200N?

    A very simple problem, I really don't know why I'm asking it.
     
  2. jcsd
  3. Feb 1, 2012 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

  4. Feb 1, 2012 #3
    Thanks for the reply, tim. "And let me say, that is a big post count"

    My paper says 20.kg so I'm rounding to two significant figures. Am I right?
     
  5. Feb 1, 2012 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    i've no idea what "20.kg" means :redface:

    i understand "20 kg" and "20.0 kg", but i've never seen "20.kg" or even "20. kg" :confused:
     
  6. Feb 1, 2012 #5

    Pengwuino

    User Avatar
    Gold Member

    Yes that is correct. When you see things like 20.kg, it means that the 0 is significant. If it were simply 20kg without the decimal, that would mean the number is only accurate to 1 significant figure. If, as tiny-tim advised, it were 20.0 kg, it would mean the second 0 is significant as well and there are 3 significant figures to take into account.

    So your answer is 200N, accurate to 2 significant figures.

    Scientific notation is really great because it clears these kind of odd notations. 20kg to 2 significant figures in SI notation would be 2.0 x 10^1 kg, clearly showing the 0 is significant.
     
  7. Feb 1, 2012 #6

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    ah! thanks, Pengwuino! :smile:
     
  8. Feb 1, 2012 #7
    Thanks, I knew something was going wrong. My teacher usually does things like that.
    I can't believe sometimes he even gets about 3-6 problems incorrectly which demonstrates unprofessional work ethic.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: What is the approximate weight of a 20.kg rock
Loading...