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Homework Help: Question that i am finding really hard

  1. Nov 16, 2006 #1
    Hi

    I tried this question a couple times, couldnt figure it out, thought maybe you guys could help.

    1. The maximum load that can safely be supported by a rope in an overhead hoist is 400N. What is the maximum acceleration that can safely be given to a 25kg object being hoisted vertically upward?

    I hope someone can help.

    Thanks
     
  2. jcsd
  3. Nov 16, 2006 #2

    Doc Al

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    What's the net force on the object if the rope is pulling as hard as it can?

    Hint: Identify all forces acting on the object.
     
  4. Nov 16, 2006 #3
    i can't figure out net force as i do not have acceleration....all i have is what is the max load the rope can take which is 400, the gravity which is -9.8 as it is going upwards and the 25 kg load
     
  5. Nov 16, 2006 #4

    Doc Al

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    First find the net force, then use it to find the acceleration.

    What forces act on the object? Hint: There are two forces acting. What is the magnitude and direction of each force?
     
  6. Nov 16, 2006 #5
    I am not sure how to find the net force. Am i right in asuming that the 2 forces acting on the object, is the downward force of m*g and the upwards force of m*-g?
     
  7. Nov 16, 2006 #6

    Doc Al

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    Gravity acts downward on the object with a force equal to mg. And, no, the upward force does not equal -mg, otherwise the net force would be zero... no acceleration at all.

    Besides gravity, what force acts on the object? Hint: Isn't the rope attached to the object?
     
  8. Nov 16, 2006 #7
    is it 400 N?

    so Fnet = 400 - mg?
     
  9. Nov 16, 2006 #8

    Doc Al

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    That's it!
     
  10. Nov 16, 2006 #9
    ok so then this is what i think the solution would be

    Fnet = 400 - mg

    a= Fnet / m
    a= (400 - (25)(9.8))/25

    and that should give me the answer i need. That does that seem right to u?
     
  11. Nov 16, 2006 #10

    Doc Al

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    Perfecto...
     
  12. Nov 16, 2006 #11
    thanks so much for the help i really appreciate it
     
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