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: Torque Rquired for stages of motion

  1. Mar 17, 2009 #1
    The fuel storage yard is seperated from the main plate by a swingbridge (swinging in a horizontal plane). The motor driving the briudge has to swing through an angle of 90degrees in 120seconds. The bridge accelerates uniformly for 40s then moves at a constant velocity, decelerating uniformly to rest in the final 20 s. The rotaing components of the bride have an equivalent moment of inertia of 400kgm² and feels a constand resisting torque of 3kN,. Find Torque of 3 stages of montion?

    How do I go about this?
    Which equations should I be using?

    Torque = Inertia x Angular acceleration
    Angular Velocity = Angle/dt (Time I presume)

    I have done


    I could then do

    Then times by Inertia (400)

    I get


    This seems too easy and whast the resisting torque value for? Do I just add this to part a, ignor for part b and take off for part c?

    Tho I'd get a negitive vale for c then?


  2. jcsd
  3. Mar 18, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    You can use the fundamental kinematics equations to develop an expression for the total rotation angle of the swing bridge, then solve for alpha1, the angular acceleration during stage 1. Once you obtain alpha1 and alpha3, you can compute the applied torque of the three stages. Are you sure your mass moment of inertia and resisting torque given above are correct? After all, 3 kN is not a torque, so what you typed doesn't make sense yet. Try it again. Post a valid attempt to get help.
  4. Mar 19, 2009 #3
    3kNm. Sorry.

    Sent what I did to my lecture and he said it was right and he oppoligsed for teh strange number sin teh question that made me have answers that I thourght must be wrong.

    All sorted

    Last edited: Mar 19, 2009
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook