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Physics B problems hard hard

  1. Nov 12, 2006 #1
    physics B problems :( hard hard

    A single cable supports an 837-kg elevator car. What is the tension in the cable when the car is moving with a) constant speed, b) an upward acceleration of 3.21 m/s^2 and c) a downward acceleration of 3.21m/s^2

    I'm not totally lost. Since the T is directed downward, I can derive from

    T=ma+mg (since g is negative)

    so I thought T would be for
    b) 873(3.21)+(873)(9.8)
    c) 873(-3.21)+873(9.8)

    is this correct?? if not someone please help me!

    next question: A truck loaded with heavy cartons is forced to stop suddenly with a deceleration of 5.0m/s^2. Calculate the minimum coefficient of frcition between the cartons and the truck bed given that the cartons do not slide.

    I thought it would just be 5. is this correct?

    and last but not least

    (ignore the mass of the scale btw)

    what will the spring scale S in the middle read when
    a) m1=1kg m2=1kg
    b) m1=1.2kg m2=1kg

    I thought it would be 1 for a) but that's not the answer.
    b), I thought it would be 1.1

    i did 1/2(m1+m2) but I don't think this is right
    someone please confirm it!!

    Last edited: Nov 12, 2006
  2. jcsd
  3. Nov 12, 2006 #2


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    a) If you're moving at a constant speed, then acceleration is 0, not 1.
    b) and c) Correct.
  4. Nov 12, 2006 #3
    so a) is just mg and b) is also correct?
  5. Nov 12, 2006 #4

    what will the spring scale S in the middle read when
    a) m1=1kg m2=1kg

    ok for this, the answer is 1.. kg? anyways its 1 something..

    b) m1=1.2kg m2=1kg

    ok how do I do this one???
    I have no idea how
  6. Nov 12, 2006 #5
    ccan someone confirm that
    b) 1.1?
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