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: Angular rotation!

  1. Jun 4, 2007 #1
    1. The problem statement, all variables and given/known data
    A 1kg engine rotates at 1 rad/sec about a point on a 3meter wire. The engine produces an acceleration of 1 rad/sec^2 and is fird for 2 minutes.

    a) What is the ω at the end of 2 minutes?
    b) what's the tension in the wire at the end of 2 min.?
    c) how far will the engine travel in meters while it's accelerating?
    d) what's the Kinetic Energy of the engine after it shuts down?

    2. Relevant equations
    a)ω=radius/Time or ω= θ/Time
    B) ???
    c) S=rθ
    θ= ωi(T)+1/2αT^2
    d) KE=1/2(Ι)(angluar acceleration)(T)^2

    3. The attempt at a solution
    a) ω=radius/Time
    ω=3/120= 0.25 rad/sec
    c) ???
    d) Ι=1/2mr^2
    Ι=1/2(1)(3)^2= 3

    KE=1/2(Ι)(angluar acceleration)(T)^2
    KE=21600 J

    need help with b&c and with corroborating a&d!
  2. jcsd
  3. Jun 5, 2007 #2


    User Avatar
    Homework Helper

    a) The engine is experiencing a constant angular acceleration, [tex]\alpha[/tex], while it is fired. The constant angular acceleration equations look similar to the constant linear acceleration equations:

    [tex]\omega = \omega _i + \alpha t[/tex]

    b) Use the final angular speed to calculate the centripetal force that the engine is experiencing, this will be the tension in the wire.

    c) your equations should do the trick

    d) I think the kinetic energy is given by

    [tex]EK = \frac{1}{2}I \omega ^2[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook