Results 1 to 3 of 3

Thread: Angular speed, linear speed, and linear speed at halfway point.

  1. #1
    Senior Member
    Joined
    Jul 2015
    From
    United States
    Posts
    481
    Thanks
    10

    Angular speed, linear speed, and linear speed at halfway point.

    rpm = 500 ; r=45cm



    (A) Angular Speed:

    to find the angular speed in units of radian/seconds I know the radian measure of a circle which is 2pirad...

    then 500 rev/60 secs x 2pirad/1rev

    I get the answer 52.35 cm

    but they are getting the answer 50pi/3?? I have no idea how they are getting that.

    (B) Find the linear speed, in units of cm/sec.

    C=2pi(45)
    C=90pi
    therefore 1 rev = 90picm

    500 rev/60 sec x 90picm/1 rev

    then I get the answer 2356.19 cm/sec

    and they get 750 pi???

    and for (C) All you have to do is divide by two which is obvious, and therefore it is 375 pi.

    What am I doing wrong??? Please explain to me what angular speed is and what linear speed is? TYVM
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    16,216
    Thanks
    3703

    Re: Angular speed, linear speed, and linear speed at halfway point.

    (a) $\omega = \dfrac{500 \, rev}{min} \cdot \dfrac{2\pi \, rad}{rev} \cdot \dfrac{1 \, min}{60 \, sec} = \dfrac{1000\pi}{60} = \dfrac{50\pi}{3} \, rad/sec$


    (b) $v = r\omega$
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor ebaines's Avatar
    Joined
    Jun 2008
    From
    Illinois
    Posts
    1,389
    Thanks
    420

    Re: Angular speed, linear speed, and linear speed at halfway point.

    Quote Originally Posted by math951 View Post
    then 500 rev/60 secs x 2pirad/1rev

    I get the answer 52.35 cm

    but they are getting the answer 50pi/3?? I have no idea how they are getting that.
    You have the same answer as the book, just wrong units - angular speed is radians/s, not cm/s:

    $\displaystyle \frac {500 \ rev}{60 \ s} \times \frac {2 \pi \ rad}{rev} = \frac {500 \pi}{30} \frac {rad} s = 52.35 \frac {rad} s$.

    Quote Originally Posted by math951 View Post
    (B) Find the linear speed, in units of cm/sec.

    C=2pi(45)
    C=90pi
    therefore 1 rev = 90picm

    500 rev/60 sec x 90picm/1 rev

    then I get the answer 2356.19 cm/sec

    and they get 750 pi???
    Again - your answer agrees with the book, because $\displaystyle 750 \pi \ cm/s= 2356 \ cm/s$
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Angular and Linear Speed
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: Apr 28th 2015, 08:58 AM
  2. Angular and Linear Speed.
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: May 8th 2013, 08:03 PM
  3. Linear/Angular Speed
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: Sep 2nd 2010, 07:43 PM
  4. Linear and Angular Speed
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: Dec 9th 2008, 09:53 PM
  5. Linear and angular speed
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: Oct 29th 2008, 11:27 PM

Search Tags


/mathhelpforum @mathhelpforum