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!

Homework Help: Physic problem

  1. Dec 9, 2006 #1
    If a wheel is turning at 3.0 rads/s, the time it takes to complete one revolution is about:

    3.0 rads/s X 1 revolution/6.28 rads = .477 revolutions/s
    now do I just times by 60s to cancel the seconds out to get 1 revolution.

    The rotational speed of the minute hand of a watch is:

    w= anglular displacement/ time
    w=2pi radian in a circle/ 3600 seconds in one rotation --> pi/1800 rad/s
    is that right?
  2. jcsd
  3. Dec 9, 2006 #2


    User Avatar
    Science Advisor
    Gold Member

    No, that would give the number of revolutions in 60 seconds. How do you think you can get an answer in seconds/revolution?

    How many seconds in a minute?
  4. Dec 9, 2006 #3
    For the first problem I just want the answer in seconds, not seconds/revolutions

    I put 3600 seconds because it is the amount of time for the minute hand to make one full revolution around the clock
  5. Dec 10, 2006 #4


    User Avatar
    Science Advisor
    Gold Member

    Understood. If the wheel makes 0.477 revolutions in 1 second, then the time it takes to make 1 rev is 1/0.477 = 2.094 seconds. You need to take the inverse of the speed (that gives sec/rev) and multiply by the number of revolutions (in this case 1).
    Oops, that's my mistake! :blushing: Your answer is correct.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook