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Homework Help: Tension on cables ? Please help?

  1. Jan 13, 2013 #1
    1. The problem statement, all variables and given/known data

    What's the tension on each cable ? and the power required to overcome tension (?)
    Here's the diagram:

    2. Relevant equations

    F=Vsin(theta) ( constant velocity ) = a= 0
    Inclined (24.25 degrees) to the horizontal plane)
    Weight of block: 25T lighter then the counterweight when pushed upwards.
    and 25T heavier when pushed downwards the inclined plane.

    Ascending and descending journey time: 4 min
    vertical height: 55m
    Average velocity calculated:

    Inclined displacement = 55M/ sin(24.25)

    Average velocity= (55m/sin(24.25))/2(60)s = 1.11 m/s on each journey upwards and downwards. ( is this right ? ) should it be divided by 4(60) instead?

    3. The attempt at a solution

    F(push) = (25 x 10^3)(9.81)sin(24.25)
    F(counterweight) = (50 x 10^3)(9.81)sin(24.25)

    Tension on cables: ((50 x 10^3)(9.81)sin(24.25)) - (25 x 10^3)(9.81)sin(24.25)

    The block is attached to the counterweight by two groups of 14 cables
    so is the tension on each group of cable = T= Total tension/2 = 50.350KN

    The power required to lift the block on each group of cable

    Work done = Tension x displacement
    Work done= 50.350 KN x 134m
    Work done= 6747.0 KN.m
    Work = 6747.0 KN.m/2(60) = 56.2 KW for each group of 14 cables.

    is this calculations correct ?
  2. jcsd
  3. Jan 15, 2013 #2
    "so is the tension on each group of cable = T= Total tension/2 = 50.350KN "
    What do you think? Can you compare this with anything else you know, in order to verify its rough value?
    You could ask/answer the same question in relation to power. What does 56 kW "look like"? Can you compare it with anything else you know, such as a car, a horse, or a kettle, say?
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