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Normal Force & Weight

  1. Oct 10, 2009 #1
    1. The problem statement, all variables and given/known data
    A 40.0 kg crate is being lowered by means of a rope. Its downward acceleration is 2.00 m/s2. What is the force exerted by the rope on the crate?

    2. Relevant equations
    Weight = mass(gravity)
    Force = mass(acceleration)

    3. The attempt at a solution
    I solved it (look at attached picture), but my answer is wrong, because the book says the answer is: 312 N. I think that I may have drawn the free-body diagram wrong; would someone please tell me where I went wrong in my free-body diagram?

    Thank you so much :) I have a test in six days & this problem will more than likely, be on it :/
     

    Attached Files:

  2. jcsd
  3. Oct 10, 2009 #2
    Well You know the the acceleration from gravity is -9.8. The actual acceleration is -2. The tension force has to account for this difference.

    I can't see the free body diagram yet but the book's answer is correct.
     
  4. Oct 10, 2009 #3
    Ahhh! Stupid mistake...I was forgetting to make the acceleration caused by gravity negative! :O
    Thank you so much! :)

    Also, I have no idea how to mark this thread "SOLVED!" I even looked in "Thread Tools" & didn't see anything ://
     
    Last edited: Oct 10, 2009
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