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Homework Help: Crane lifting crate

  1. Mar 19, 2007 #1
    1. The problem statement, all variables and given/known data

    The crane shown in the drawing is lifting a 186-kg crate upward with an acceleration of 2.0 m/s2. The cable from the crate passes over a solid cylindrical pulley at the top of the boom. The pulley has a mass of 130 kg. The cable is then wound onto a hollow cylindrical drum that is mounted on the deck of the crane. The mass of the drum is 150 kg, and its radius is 0.76 m. The engine applies a counterclockwise torque to the drum in order to wind up the cable. What is the magnitude of this torque? Ignore the mass of the cable.

    2. Relevant equations

    torque= I*angular acceleration
    I= mr^2
    angular accel= accel/r

    3. The attempt at a solution

    I tried everything that i know

    angular accel= 2/.76 =2.6316 rad/s^2
    I=150*.76^2= 86.64
    torque= 86.64*2.6316= 228 N*m

    But this answer is wrong. I tried negitive and thats wrong. What am I doing wrong! lol.
  2. jcsd
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