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Homework Help: Motion & Beams Problem

  1. Mar 25, 2007 #1
    Appreciate if someone could take the time to look at the following problem, my answers, and can point out where I have went wrong. Also, part 4, I think more info. is needed to determine this, but I may be wrong. Anyway, here goes:

    A hoist motor is attached to a support beam as shown in the diagram. The hoist lifts a load of 3.5kg, the load starts from rest and has a final velocity of 2 m/s after 4 seconds. The motor can develop a torque of 4 Nm.
    i) The linear acceleration of the mass
    ii) The angular acceleration of the motor
    iii) The force on the beam at M when the hois is lifting the load
    iv) The reaction forces RA and RB on the beam supports A and B

    My attempt at solutions:
    i) Linear acceleration (a) = (final velocity - initial velocity) / time
    = (2 - 0)/4
    = 0.5 m/s/s

    ii) Work done in 4 seconds = 0.5mv^2
    = 0.5 * 3.5 * 2^2
    = 7 Joules
    Angle of rotation = Work / Torque
    = 7/4
    = 1.75 radians in 4 seconds
    Angular acceleration = 0.4375 radians/s/s

    iii) Force = mass * acceleration = 3.5 * (9.81 + 0.5)
    = 36.085 N

    iv) Don't know how to tackle this part as it is.

    Sketch can be found here
    http://img443.imageshack.us/img443/5980/q2mplg7.jpg [Broken]
    Last edited by a moderator: May 2, 2017
  2. jcsd
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